記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.chemmater.1c00872

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jallcom.2021.159548

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.ceramint.2021.03.129

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.mtener.2020.100492

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.ceramint.2020.07.085

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this work, several X-ray and nuclear analysis techniques were used to examine ZnO materials co-doped with In and Ga, or IGZO materials. X-ray diffraction analysis, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy revealed multi-scale defects in the materials. A nanoscale secondary Ga₂Zn₉O₁₂ spinel phase, mesoscale grain boundaries, and atomic-scale lattice defects were detected. The lattice defects included oxygen vacancies, zinc vacancies, and complex defects. Positron annihilation spectroscopy and Doppler broadening spectroscopy provided evidence of interactions between charge carriers and defects sites, which explained the low thermal conductivities of the IGZO materials (κ_total ≈ 3.9 W/mK) at 773 K. This combination of X-ray and nuclear analytical techniques can be viewed as a novel approach for investigating the thermoelectric properties of materials with complex crystal structures that contain atomic-scale voids, nanoscale secondary phases, and mesoscale grain boundaries.

DOI： 10.1016/j.ceramint.2020.01.084

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jallcom.2020.156119

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Compound semiconductors derived from ZnS (zincblende and wurtzite) with tetrahedral framework structures have functions for various applications. Examples of such materials include Cu–S-based materials with zincblende-derivative structures, which have attracted attention as thermoelectric (TE) materials over the past decade. This study illuminates superior TE performance in polycrystalline samples of enargite Cu₃P_1−xGe_xS₄ with a wurtzite-derivative structure. The substitution of Ge for P dopes holes into the top of the valence band composed of Cu-3d and S-3p, whereby its multiband characteristic leads to a high TE power factor. Furthermore, a reduction in the grain size to 50–300 nm can effectively decrease phonon mean free paths, leading to low thermal conductivity. These features result in a dimensionless TE figure of merit ZT of 0.5 at 673 K for the x = 0.2 sample. Environmentally benign and low-cost characteristics of the constituent elements of Cu₃PS₄, as well as its high-performance thermoelectricity, make it a promising candidate for large-scale TE applications. Furthermore, this finding extends the development field of Cu–S-based TE materials to those with wurtzite-derivative structures.

DOI： 10.1002/adfm.202000973

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this work, we have reported the thermoelectric performance of graphene-zinc oxide hybrid cement composites for the first time. Nanostructured graphene and zinc oxide were incorporated into cement to increase the thermoelectric properties of cement composites. The as-received materials were blended, compressed, and subsequently cured at room temperature to make it bulk. On bulk samples, electrical conductivity, Seebeck coefficient, and thermal conductivity were measured. As a consequence of high electrical conductivity and the Seebeck coefficient, the composites exhibited a high value of thermoelectric efficiency. The maximum figure of merit (ZT) of 0.01 is obtained when the contents of graphene and ZnO are 10 wt%, respectively, by mass of cement. This ZT is the highest reported to date for the thermoelectric cement composites, a nearly 70% increase over the previous record with carbon based inclusions. High figure of merit is crucial for energy harvesting applications in future buildings.

DOI： 10.1016/j.energy.2020.117396

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Nanoporous Fe₃O₄ composites containing metallic Cu nanoparticles were synthesized by reducing-leaching treatment of CuFe₂O₄ precursor. Thermoelectric properties of the composites sintered at 1270 ºC greatly improved compared with Fe₃O₄ without Cu, presumably due to a nanoporous structure and the Cu nanoparticles remaining in the Fe₃O₄ matrix after acid leaching. The electrical and thermal conductivity indicate that Cu in the matrix promotes the electron conduction and suppresses the phonon conduction, improving the dimensionless figure-of-merit, ZT.

DOI： 10.5109/2740934

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Famatinite Cu₃SbS₄ has attracted attention for its potential application in thermoelectric (TE) contexts. In this work, we report the impacts of co-substituting Ge and P for Sb on TE properties. Melting and heat treatment methods were adopted to synthesize samples of Cu₃Sb_1-x-yGe_xP_yS₄ (x ≤ 0.4, y ≤ 0.3). In this system, Ge functioned as an acceptor for doping a hole to the valence band, which led to enhancement of the TE power factor. Contrastingly, P barely altered the electronic structure. Furthermore, both Ge and P acted as point defects, which effectively decreased lattice thermal conductivity. The combined effects of the co-substitution gave rise to an enhanced dimensionless figure of merit, ZT, of 0.67 at 673 K.

DOI： 10.1039/c9cp06233e

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Cement based thermoelectric materials can convert the available ambient heat absorbed by the building surfaces in summer into electrical energy. These materials can have an impact on the improvement of indoor climate of buildings, reduction of energy consumption and energy harvesting applications especially in the urban areas. In this paper, the thermoelectric properties of cement based composites with graphene nanoplatelets (GNP) inclusions were reported for the first time. GNP-cement mixtures were prepared by planetary ball milling and compressed subsequently to form bulk composites. We report the maximum electrical conductivity of 16.2 Scm⁻¹ and Seebeck coefficient of +34.0 µVK⁻¹ in this work. Hall measurement was performed to determine the material type and carrier concentration. It was found that all specimen exhibit p-type semiconductor behavior. Thermal diffusivity measurements were carried out using laser flash measurement technique. The highest figure of merit 0.44 × 10⁻³ was achieved at about 70 °C. Enhanced thermoelectric properties of graphene nanoplatelets cement based composites have a promising prospect in the urban heat island effect alleviation, thus saving electricity consumption and energy harvesting.

DOI： 10.1016/j.enbuild.2019.109419

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report the electronic structure and thermoelectric properties of a tin titanium trisulfide, Sn_1.2Ti_0.8S₃. The crystal structure is composed of infinite "ribbons" of double edge-sharing (Sn⁴⁺/Ti⁴⁺)S₆ octahedra capped by Sn²⁺. First-principles calculations predict a nearly unidirectional transport of electrons along the ribbon axis for a single crystal and the existence of lone-pair electrons on Sn²⁺. Experiments on polycrystalline pressed samples demonstrate that Sn_1.2Ti_0.8S₃ exhibits semiconducting temperature dependence of electrical resistivity and a large negative Seebeck coefficient at room temperature. Substitution of Nb⁵⁺
for Sn⁴⁺ at the octahedral sites increases the electron carrier concentration, leading to an enhancement of the thermoelectric power factor. Anisotropy in the electronic properties is weak because of a weak orientation of the ribbon axis of crystallites in the pressed sample. The lattice thermal conductivity is less than 1 W K^-1m^-1 for the pristine and substituted samples, which is attributed to weak bonding between the ribbons via the lone-pair electrons of Sn²⁺ and to random occupation of S⁴⁺, Ti⁴⁺, and Nb⁵⁺ at the octahedral sites.

DOI： 10.1063/1.5093183

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Copper-based chalcogenides with tetrahedral framework structures have been attracting increasing attention as environmentally friendly thermoelectric materials. A representative group of such thermoelectric chalcogenides is the Cu ₂₆ A ₂ M ₆ S ₃₂ (A = V, Nb, Ta; M = Ge, Sn) family of colusites, which exhibit low electrical resistivity, a large Seebeck coefficient, and low thermal conductivity; these properties are necessary for efficient thermal-to-electronic energy conversion. Here, we show the impact of crystal structure on the lattice thermal conductivity of colusite with A = Nb, M = Sn. The crystal structure can be modified by controlling the cationic compositions and the deficiency in the sulfur content as Cu _26-x Nb ₂ Sn _6+x S _32-δ . The Cu/Sn ratio is found to be the key parameter for exsolution into distinct phases with ordered and disordered arrangements of cations. For the ordered-structure phase, sulfur sublimation induces atomic-scale defects/disordered states including interstitial defects, anti-site defects, and site splitting, which function as strong phonon scatterers, and the lowest lattice thermal conductivity of ∼0.5 W K ^-1 m ^-1 is achieved for the modified ordered structure. This finding provides a simple approach to modifying the crystal structure of thermoelectric chalcogenides via the loss of anions to reduce their lattice thermal conductivity.

DOI： 10.1039/c8ta08248k

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report the preparations, thermoelectric and magnetic properties, and electronic structures of Cu-Ti-S systems, namely, cubic thiospinel c-Cu_1-xTi₂S₄ (x ≤ 0.375), a derivative cubic and Ti-rich phase c-Cu_1-xTi_2.25S₄ (x = 0.5, 0.625), and a rhombohedral phase r-CuTi₂S₄. All samples have the target compositions except for r-CuTi₂S₄, whose actual composition is Cu_1.14Ti_1.80S₄. All of the phases have n-type metallic character and exhibit Pauli paramagnetism, as proven by experiments and first-principles calculations. The Cu and Ti deficiencies in c-Cu_1-xTi₂S₄ and r-CuTi₂S₄, respectively, decrease the electron-carrier concentration, whereas the "excess" of Ti ions in c-Cu_1-xTi_2.25S₄ largely increases it. For r-CuTi₂S₄, the reduced carrier concentration increases the electrical resistivity and Seebeck coefficient, leading to the highest thermoelectric power factor of 0.5 mW K^-2m^-1 at 670 K. For all of the Cu-Ti-S phases, the thermal conductivity at 670 K is 3.5-5 W K^-1m^-1, where the lattice part of the conductivity is as low as 1 W K^-1m^-1at 670 K. As a result, r-CuTi₂S₄ shows the highest dimensionless thermoelectric figure of merit ZT of 0.2. The present systematic study on the Cu-Ti-S systems provides insights into the structural design of thermoelectric materials based on Cu-M-S (M = transition-metal elements).

DOI： 10.1021/acs.inorgchem.8b02955

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s13391-018-0062-x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jssc.2017.12.031

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s11664-015-4179-5

記述言語：英語  

Rapid progress in thermoelectric performance of oxide materials has been conducted virtually exclusively in Japan, resulting in more than ten times increase in the ZT values of oxides within the last two decades. This has caused a revolutionary change in the guiding principles of thermoelectric materials research, in which oxide materials had been disregarded as a potential candidate until early 1990s. Promising oxide thermoelectric materials having been discovered include CaMnO 3 -based perovskites, Al-doped ZnO, layered cobalt oxides represented by NaCo₂O₄ and Ca₃Co₄O₉, and SrTiO 3 -related phases. This chapter reviews the current aspects of bulk oxide thermoelectric materials, and some strategies for selective reduction of the lattice thermal conductivity (selective phonon scattering) in bulk oxides are also discussed.

DOI： 10.1007/978-3-319-14478-8_7

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s11664-012-2382-1

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In our facile synthesis method, poly(vinylpyrrolidone) protected Pt and Pt-Pd bimetallic nanoparticles with controllable polyhedral core-shell morphologies are precisely synthesized by the reduction of Pt and Pd precursors at a certain temperature in ethylene glycol and silver nitrate as structure-controlling agent. The Pt nanoparticles exhibited well-shaped polyhedral morphology with highly fine and specific nanostructures in the nanosized range of 20 nm. Important evidences of core-shell configurations of the Pt-Pd core-shell nanoparticles were clearly characterized by high-resolution transmission electron microscopy (HRTEM) measurements. The results of HRTEM images showed that the core-shell Pt-Pd nanoparticles in the nanosized range of 25 nm with polyhedral morphology were synthesized with the thin Pd shells of the nanosized range of about 3 nm in thickness as the atomic Pd layers grown on the as-prepared Pt cores in the nanosized range. The very interesting characterization of surface structure of Pt nanostructures and Pt-Pd core-shell nanostructures with surface defects were observed. The high-resolution TEM images of Pt-Pd bimetallic nanoparticles showed that the Frank-van-der Merwe and Stranski-Krastanov growth modes coexist in the nucleation and growth of the Pd shells on the as-prepared Pt cores. The lattice-fringe spacing was estimated as around 0.240 nm, which is assigned exactly to the lattice-fringe spacing of the {111} planes of the Pd metal shell observed. It is predicted that the FM growth becomes a more favorable growth mode compared to the SK growth in the formation of the very thin Pd shells of Pt-Pd core-shell nanoparticles. The experimental evidences of the deformations of lattice fringes and lattice-fringe patterns were found in polyhedral Pt nanoparticles as well as polyhedral Pt-Pd core-shell nanoparticles. The interesting re-nucleation and re-crystallization at their connections or their attachments of the as-prepared nanoparticles are found in a good lattice match. In addition, our novel ideas of the largest surface-area superlattices and suitable utilization of such large surface areas are proposed for next generations of various fuel cells with low cost. Finally, the products of as-prepared Pt-Pd core-shell nanoparticles can potentially utilized as highly efficient catalysts in the realization of polymer electrolyte membrane cell (PEMFC) and direct methanol fuel cell (DMFC) using the very low Pt loading with better cost effective design.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/C2NJ40027H

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Polycrystalline samples of (Ca_1-xR_x)₃Co₂O₆ with R = Gd, Tb, Dy and Ho at x = 0 - 0.1 were synthesized and the effects of rare earth substitution on their thermoelectric properties were investigated. In the high-temperature region, the rare earth substitution resulted in an increase in the Seebeck coefficients (S), and the S values increased with decreasing ionic radius of rare earth elements in the order Gd³⁺>Tb³⁺>Dy³⁺>Ho³⁺ . In contrast, the influence of rare earth substitution on the electrical resistivity was small. The high-temperature power factor was thereby improved by the late rare earth substitutions, particularly those with Ho³⁺ for Ca²⁺. For the Ho-doped samples (x ≤ 0.05), the power factor was significantly improved by increasing Ho concentration.

DOI： 10.1016/j.ssc.2006.05.033

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A series of nine bulk crystals of the Zn_{4 - x}Cd _xSb₃ compounds (x = 0-2.00 with 0.25 step) has been successfully synthesized and the detailed crystal structure has been refined by powder XRD study using the Rietveld method including the quantitative analysis. The substitution limit of the Cd atoms for the Zn_{4 - x}Cd _xSb₃ system has been extended to x = 2.00 by employing the vacuum casting method without annealing. The purities and densities of the bulk crystals exceeded approximately 96 mass% and 95% of XRD density, respectively. The lattice parameters of the a and c-axes in the system increase linearly with increasing Cd content x with obeying the Vegard law.

DOI： 10.1016/j.jallcom.2005.06.062

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Exchange and Innovation Conference on Engineering and Sciences  

The Magnéli phase W18O49 exhibits promising thermoelectric properties owing to its high electrical conductivity and low thermal conductivity, despite its low Seebeck coefficient. In this study, (W1-xCox)18O49 (0 ≤ x ≤ 0.05) was synthesized via a solid-state reaction, followed by spark plasma sintering, to investigate the effect of cobalt dopants on the thermoelectric properties of W18O49. The XRD analysis indicated the formation of W18O49-based phase and the secondary phase CoWO4. The cobalt substitution decreased both the electrical and thermal conductivities while slightly increased the Seebeck coefficient. These reduction in the thermal conductivity led to enhanced thermoelectric performance. The dimensionless figure of merit (ZT) reached to 0.022 at 1073 K for x = 0.05.

DOI： 10.5109/7323399

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Exchange and Innovation Conference on Engineering and Sciences  

TE materials are highly regarded for their exceptional ability to efficiently convert waste heat into electricity, making them the most profitable type of energy harvesting materials. Oxide-based materials are highly promising due to their advantageous characteristics such as their large elemental abundance, nontoxicity, and good thermal stability. Zinc oxide shows outstanding thermal stability throughout a wide temperature range, as well as high Seebeck coefficient. These features render ZnO a highly promising candidate for TE applications. However, the TE performance of the oxide is limited by its extremely high thermal conductivity and limited electrical c0onductivity. Numerous strategies have been thought of to deal with these problems, and the investigation emphasized doping approaches. This review offers valuable insights for researchers who are fascinated by the subject of TEmaterials and their applications.

DOI： 10.5109/7323405

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記述言語：英語   出版者・発行元：International Exchange and Innovation Conference on Engineering and Sciences  

Thermoelectric (TE) energy conversion generates electricity directly from a heat flux penetrating a solid device consisting of n- and p-type semiconductors. However, limitations in elemental abundance and poor thermal durability of conventional TE materials have prevented a wide commercialization of the TE power generation. Metal oxides are highly durable at high temperature in air, and are generally non-toxic, low cost with minimal environment impact. Boosted by the global environment issues and carbon dioxide mitigation problems, oxide TE materials are becoming more and more of vital importance for recuperation of decentralized waste heat energy for higher total energy efficiency. In this paper, nanostructure engineering in TE oxides will be depicted with focuses on thermal conductivity reduction by introducing complex microstructure, and by carefully choosing the crystal structure. The former approach is exemplified by multinary-doped ZnO with a spontaneously formed microstructure in sintered bodies, while the latter strategy is demonstrated by an ultra_low lattice thermal conductivity found in β-pyrochlore (defect pyrochlore) oxides with an oversized cage-like structure surrounding a small atom inside. Current issues of TE oxides will be discussed with a future prospect of the materials and applications.

DOI： 10.5109/7323430

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CiNii Research

記述言語：英語   出版者・発行元：International Exchange and Innovation Conference on Engineering and Sciences  

Thermoelectric materials convert heat energy into electrical energy. They have the potential to be used in a variety of applications, including power generation, waste heat recovery, and temperature control. Several transition metal suboxides, also known as Magnéli phases, are a promising class of thermoelectric materials because of their high electrical conductivity, low thermal conductivity, and chemical stability. In this review article, we discuss the Magnéli phase of five different transition metal suboxides: titanium suboxide (TiOx), tungsten suboxide (WOx), molybdenum suboxide (MoOx), vanadium suboxide (VOx), and niobium suboxide (NbOx). We focus on their crystal structure, electrical and thermal properties, and potential applications as thermoelectric materials. We conclude that the Magnéli phases have the potential to be high-performance thermoelectric materials. However, further research is needed to optimize their properties and develop new synthesis methods.

DOI： 10.5109/7157998

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CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemistry of Materials  

Copper-based sulfide semiconductors with the structure based on a sphalerite-like network can provide environmentally sound solutions to thermoelectric and photovoltaic energy conversion at a low cost. In this study, we report the synthesis and characterization of a copper-based sulfide, Cu30Ti6Sb2S32, discovered within the pseudobinary Cu3SbS4-Cu4TiS4 system. This new compound crystallizes in a colusite-like cubic structure, which is characterized by “interstitial” Ti atoms forming tetrahedral-octahedral [TiS4]Cu6 complexes linearly arranged within the Cu-S corner-sharing matrix. The [TiS4]Cu6 unit arrangement distinguishes the crystal structures of Cu26Ti2Sb6S32 (isolated units, 0D linkage), Cu30Ti6Sb2S32 (chain of linked units, 1D), and Cu4TiS4 (plane of linked units, 2D). We emphasize the semiconducting nature and the low thermal conductivity. The electronic structure and vibrational properties are investigated by the combination of experiments and first-principles calculations. We demonstrate that a design approach based on the pseudobinary composition, here, with the generic formula (Cu3SbS4)1-x(Cu4TiS4)x, is a fruitful direction for the discovery of new copper-based sulfides with tunable transport properties.

DOI： 10.1021/acs.chemmater.3c01135

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記述言語：英語  

DOI： 10.5551/jat.63337

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PubMed

記述言語：英語   出版者・発行元：公益社団法人 日本セラミックス協会  

Zinc oxide (ZnO) thermoelectric ceramics were consolidated by spark plasma sintering (SPS) along with one-step/two-step sintering (OS/TS) temperature profiles, the latter employing a strategy of heating to a higher temperature (T1) followed by prolonged sintering at a lower temperature (T2) for densification while preventing grain growth. In the first step, the temperatures and holding times were 1100 and 1150 °C for 15 and 5 min, respectively, and the second-step was maintained at 1050 °C for 30, 60, and 120 min. By combining TS and SPS processes (TS-SPS), high relative densities of 91.494.9 % were achieved without significant grain growth. Electron backscatter diffraction (EBSD) revealed a noticeable grain-growth suppression of 56 % for the TS-SPS sample with T1 = 1100 °C. The highest power factor of 7.8 × 1015 W K12 m11 was achieved for the TS-SPS ZnO, while the lowest thermal conductivity of 4.7 W K11 m11 was achieved for the OS-SPS ZnO, attaining a figure of merit (ZT) of 0.017 at 775 °C.

DOI： 10.2109/jcersj2.22097

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CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Science  

α-MgAgSb has been receiving attention as a thermoelectric material due to its high performance at 300–550 K. A MgAgSb sample synthesized by melting the constituent elements is known to contain secondary phases, which can be diminished by long-term heat treatment. However, less effort has been devoted to investigating the secondary phases and exploring an effective synthesis route to improve the sample purity. In this work, we showed that an as-melted sample comprised α-MgAgSb and large amounts of Ag3Sb and Mg4AgSb3. The secondary phases were successfully diminished/reacted through short-term ball milling and sintering processes. Secondary phases were further reduced by decreasing the starting Ag content, leading to the enhanced dimensionless figure of merit ZT of 0.4 at 300 K and 0.7 at 450 K. The synthesis route without long-term heat treatment is expected to contribute to efficient production of α-MgAgSb. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s10853-022-07306-5

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その他リンク： https://link.springer.com/article/10.1007/s10853-022-07306-5/fulltext.html

掲載種別：研究論文（学術雑誌）   出版者・発行元：Ceramics International  

In single-doped [Zn(1−y)Iny]O (y = 0.005, 0.01, 0.02, 0.03, 0.05) ceramics and In and Ga dual-doped [Zn(1−x−y)GaxIny]O (y = 0.005; x = 0.005, 0.01, 0.02, 0.03, 0.05) ceramics were prepared using a solid-state reaction and spark plasma sintering at 1423 K in vacuum. The microstructural and chemical composition analyses revealed that Zn7In2O10 and ZnGa2O4 existed as the secondary phases in the single-doped ZnO (y ≥ 0.02) and dual-doped ZnO (y = 0.005; x ≥ 0.02) ceramics. Doped (single and dual) ZnO showed a high relative density of 92.5–100% as compared to pure ZnO (91.3%). The dual-doped sample with x = 0.005 and y = 0.005 prepared at 1046 K showed the highest power factor of 1.05 mW K−2 m−1. The dual-doped ZnO ceramics thereby showed an improved thermoelectric performance, attaining the figure of merit of 0.17 as compared to that of pure ZnO (0.12) at 1046 K.

DOI： 10.1016/j.ceramint.2022.01.334

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Solid State Chemistry  

Low lattice thermal conductivity is observed in compounds having disordered atomic configurations in their crystal structures. At temperatures above 300 ​K, a Cu–S-based semiconducting compound, Cu3.1Nb0.25Sn0.9S4, with a sphalerite-derived disordered structure, exhibits thermal conductivity less than 1 ​W ​K−1 ​m−1. In this study, we synthesized and tested the thermoelectric properties of the hole-doped derivatives, Cu3.1Nb0.25−xTixSn0.9S4 (x ​= ​0, 0.125, 0.25) and Cu3.1Ti0.1875Sn0.9S4, up to 673 ​K. The hole-carrier doping decreased the electrical resistivity, improving the power factor. Cu3.1Ti0.25Sn0.9S4 shows a dimensionless figure of merit ZT of 0.1/0.6 ​at 300/673 ​K due to its inherent low lattice thermal conductivity and improved power factor. The thermoelectric properties of the Cu3.1Nb0.25Sn0.9S4-based compounds were compared with those of Cu3SbS4-based compounds with an ordered arrangement of Cu atoms in a similar sphalerite-derived structure, showing that the disordered atomic arrangement is responsible for the enhanced scatterings of both phonons and electrons.

DOI： 10.1016/j.jssc.2022.122960

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the European Ceramic Society  

High-temperature thermoelectric properties of tungsten-based Magnéli phase oxide (W1-xTix)18O49 (0 ≤ x ≤ 0.25) prepared by solid state reaction followed by densification via spark plasma sintering (SPS) were studied. The Ti substitution increased the Seebeck coefficient, the power factor, and decreased both the electronic and lattice thermal conductivity. The synergistic substitution effect on the electrical and thermal properties and inherently low total thermal conductivity of 1.46 ± 0.08 WK−1 m−1 originating from the tunnel-like crystal structure of the oxide led to a significantly high ZT of 0.50 ± 0.07 at 1073 K for the sample with x = 0.2.

DOI： 10.1016/j.jeurceramsoc.2021.12.014

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The nanoparticles of Al-doped ZnO were successfully grown into rod-like and platelet-like morphologies by soft chemical routes. These powders were consolidated using spark plasma sintering (SPS) technique. The samples consolidated from rods and platelets exhibited characteristic structures with preferential orientation while the sample consolidated from nanoparticles did not show any sign of preferential orientation. The measured ZT values along the preferred orientation directions were found to be 0.16 and 0.25 at 1223 K for the samples consolidated from rods and platelets, respectively. The sample consolidated from nanoparticles exhibited fine grains and highly distributed nanoprecipitates, resulting in a ZT value of 0.3 at 1223 K due to the lower thermal conductivity resulting from nanostructuring. Using the simple parabolic band model and Debye-Callaway thermal transport model, the anisotropic properties of the nanostructured samples were elucidated and the influence of the grain size and nanoprecipitates on the electron and phonon transport was analyzed and discussed in detail.

DOI： 10.1039/c3ra47617k

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2320/matertrans.MPR2014904

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The thermoelectric properties of the double-perovskite-type oxide Sr ₂ MnMoO ₆ were investigated in terms of La doping at the A-site of the oxide. The Bragg reflection of Sr _2-x La _x MnMoO ₆ was indexed with a monoclinic unit cell and the structure was determined in the monoclinic space group P2 ₁ /n, due to the good agreement between the observed and calculated patterns after Rietveld refinement. The electrical conductivity of the oxides, σ, showed a semiconductor characteristic, increasing monotonically from 0.1 to 0.5S/cm at room temperature to 5-50S/cm at 1250K. The Seebeck coefficient, S, indicated the oxides to be of n-type. The absolute values of S increased with increasing temperature. These absolute values increased at just x=0.1, and then drastically decreased with increasing x ranging from 0.3 to 1.0. The power factor of the oxides, S ² σ, increased with increasing temperature; Sr _1.9 La _0.1 MnMoO ₆ showed approximately 0.12mW/mK ² at 1250K, which is the largest value among all the samples examined in this study. The thermal conductivities of the oxides showed a temperature independent behavior, ranging approximately 0.6-1.0W/mK, and the values were significantly low. The dimensionless figure of merit, ZT=S ² σT/κ, increased with the increasing temperature. The highest ZT value of 0.13 was observed for Sr _1.9 La _0.1 MnMoO ₆ at 1100K.

DOI： 10.1016/j.jascer.2013.06.006

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this review, we present the synthesis and characterization of Pt, Pd, Pt based bimetallic and multi-metallic nanoparticles with mixture, alloy and core-shell structure for nano-catalysis, energy conversion, and fuel cells. Here, Pt and Pd nanoparticles with modified nanostructures can be controllably synthesized via chemistry and physics for their uses as electro-catalysts. The cheap base metal catalysts can be studied in the relationship of crystal structure, size, morphology, shape, and composition for new catalysts with low cost. Thus, Pt based alloy and core-shell catalysts can be prepared with the thin Pt and Pt-Pd shell, which are proposed in low and high temperature proton exchange membrane fuel cells (PEMFCs), and direct methanol fuel cells (DMFCs). We also present the survey of the preparation of Pt and Pd based catalysts for the better catalytic activity, high durability, and stability. The structural transformations, quantum-size effects, and characterization of Pt and Pd based catalysts in the size ranges of 30 nm (1-30 nm) are presented in electro-catalysis. In the size range of 10 nm (1-10 nm), the pure Pt catalyst shows very large surface area for electro-catalysis. To achieve homogeneous size distribution, the shaped synthesis of the polyhedral Pt nanoparticles is presented. The new concept of shaping specific shapes and morphologies in the entire nano-scale from nano to micro, such as polyhedral, cube, octahedra, tetrahedra, bar, rod, and others of the nanoparticles is proposed, especially for noble and cheap metals. The uniform Pt based nanosystems of surface structure, internal structure, shape, and morphology in the nanosized ranges are very crucial to next fuel cells. Finally, the modifications of Pt and Pd based catalysts of alloy, core-shell, and mixture structures lead to find high catalytic activity, durability, and stability for nano-catalysis, energy conversion, fuel cells, especially the next large-scale commercialization of next PEMFCs, and DMFCs.

DOI： 10.1166/jnn.2013.7570

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In our present research, bottom-up self-assembly of gold (Au) nanoparticles on a flat copper (Cu) substrate is performed by a facile method. The very interesting evidence of self-assembly of Au nanoparticles on the top of the thin assembled layer was observed by scanning electron microscopy (SEM). We had discovered one of the most general and simple methods for the self-assembly of metal nanoparticles. The general physical and chemical mechanisms of the evaporation process of the solvents can be used for self-assembly of the as-prepared nanoparticles. The important roles of molecules of the used solvents are very critical to self-assembly of the as-prepared Au nanoparticles in the case without using any polymers for those processes. It is clear that self-assembly of such one nanosystem of the uniform Au nanoparticles is fully examined. Finally, an exciting surface plasmon resonance (SPR) phenomenon of the pure Au nanoparticles in the solvent was fully discovered in their exciting changes of the narrow and large SPR bands according to synthesis time. The SPR was considered as the collective oscillation of valence electrons of the surfaces of the pure Au nanoparticles in the solvent by incident ultraviolet-visible light. Then, the frequency of light photons matches the frequency of the oscillation of surface electrons of the Au nanoparticles that are excited.

DOI： 10.1155/2013/793125

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A systematic investigation on the microstructure and thermoelectric properties of Al-doped ZnO using α- and γ-Al₂O ₃ as dopants was conducted in order to understand the doping effect and its mechanism. The samples were prepared by the spark plasma sintering technique from precursors calcined at various temperatures. Clear differences in microstructure and thermoelectric properties were observed between the samples doped with α- and γ-Al₂O₃. At any given calcination temperature, γ-Al₂O₃ resulted in the formation of a larger amount of the ZnAl₂O₄ phase in the Al-doped ZnO samples. The average grain size was found to be smaller for the γ-Al₂O₃-doped samples than that for the α-Al₂O₃-doped ones under the same sintering condition. It is proposed that the ZnAl₂O₄ phase is the reason for the observed suppression of grain growth and also for the slightly reduced lattice thermal conductivity exhibited by these samples. The γ-Al₂O₃ promoted the substitution for donor impurities in ZnO, thus resulting in shrinkage of the unit cell volume and an increase in the electrical conductivity compared with the α-Al ₂O₃-doped ZnO. At a calcination temperature of 1173 K, the γ-Al₂O₃-doped sample showed a ZT value of 0.17 at 1173 K, which is 27% higher than that of the α-Al₂O ₃-doped sample.

DOI： 10.1016/j.jallcom.2012.12.091

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1080/17458080.2012.755868

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this review, we have investigated research results of recent patents of various kinds of Pt or Pd based nanoparticles for catalysis. It includes aspects of practical applications of metal, bimetal or multi-metal based nanoparticles in catalysis and fuel cells. The synthetic methods and catalysts engineering are comprehensively presented in their excellent applications for fuel cells. The aims of this review are to provide achievements and highlights of patents of recent applications of Pt or Pd based material catalysts for various fuel cells. In particular, the Pt or Pd based nanoparticles of certain size, shape, structure, composition show great and promising applications in fuel cells and energy issues. The new and modified catalysts associated with the Pt or Pd based nanoparticles can improve future fuel cells with very high and robust performance. Our ideas and proposals of using a very low weight of Pt metal in novel robust and efficiently designed catalysts are one of the best ways for the large-scale commercialization of fuel cells technology. In addition, the characterization and controlled synthesis of metal, bimetal, multi-metal, and multi-component nanoparticles are discussed in potential applications for fuel cells. Finally, we think that greatly novel discoveries in science and technology through succesful synthesis of novel alloy or core-shell nanoparticles and their excellent applications in catalysis, medicine and biology can be clearly predicted.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In our research, the preparation processes of Pd nanoparticles (Pd NPs) with different methods by adding a certain amount of silver nitrate, iron chloride or sodium iodide are presented in order to control their size and morphology. Various sizes and shapes of Pd NPs are observed by alcohol reduction. The results show the size and morphology control of Pd NPs with chemical reductions of Pd salts by ethanol and ethylene glycol (EG) that have very different reduction processes. The modified polyol method with the gradual addition of Pd and polyvinylpyrollidone precursors in EG at 160°C has led to control their size and morphology in the 10 nm range using 0.02 M AgNO₃. It is observed that the Pd nanorod is also formed. The main factors that will control the shapes of Pd NPs have been presented to explain their growth and formation mechanisms in a control process.

DOI： 10.1080/17458080.2010.543988

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In our research, Pt nanoparticles by polyol method using AgNO₃ were studied by UV-vis-IR spectroscopy, X-ray diffraction analysis, transmission electron microscopy (TEM) and high-resolution (HR) TEM methods. Their specific surfaces were investigated in the controlled size and morphology in the range of 10 nm without AgNO₃, and in the range of 20 nm with AgNO ₃. Here, AgNO₃ is crucial to appearance of polyhedral Pt nanoparticles but their convex or concave roughness characterizations are confirmed in the range of 20 nm without AgNO₃. The high crystallization degree of the as-prepared Pt nanoparticles was discovered in the HRTEM evidences. In addition, the interesting complexity of surface roughness showed important evidences of bonding and chemical changes. Re-nucleations and re-crystallizations at their connections by surface attachment were discovered. The results show importance of controlling size and morphology, and big challenge for HRTEM method is predicted, which is how to measure many nanoparticles with high resolution with good quality of fine lattice-fringe systems around 10 nm.

DOI： 10.1166/jamr.2012.1103

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this paper, the polyhedral Pt nanoparticles were prepared by a modified polyol method using AgNO₃ as a nanostructure-shaping agent. TEM and HRTEM images of Pt nanoparticles show the particle size in the 10 nm range for the well-controlled case. In contrast, Pt nanoparticles have the particle size in the 50 nm range for the uncontrolled case. To understand the important issues of morphology, size, surface and structure, the as-prepared Pt nanoparticles were investigated through UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution (HR)TEM measurements. In the two cases, the as-prepared Pt nanoparticles with and without the control procedures exhibit surface attachment, aggregation or agglomeration and assembly. The mechanisms can lead to the formation of the ultra-porous mesostructure of the as-prepared Pt nanoparticles by using various sophisticated control methods. Therefore, the experimental findings and observations showed the formations of the porous Pt nanostructures as the new Pt textures from self-aggregation or self-agglomeration and self-assembly of extreme importance in designing great superlattices under experimentally chemical and physical methods. This also proved the important role of PVP polymer in the protection of the as-prepared nanoparticles. In particular, a new phenomenon was found in the randomly natural collapse and self-breaking in the Pt nanostructures originating from the naked Pt nanoparticles without protective polymer agents. As a result, a porous meso-nanostructure was formed by the structural changes of Pt nanoparticles without stabilization of the PVP polymer. Finally, the discoveries of surface structure changes of polyhedral Pt shapes and morphologies in future are very important in further catalysis investigation.

DOI： 10.1039/c2nj40027h

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In our facile synthesis method, poly(vinylpyrrolidone)-protected Pt and Pt-Pd bimetallic nanoparticles with controllable polyhedral core-shell morphologies are precisely synthesized by the reduction of Pt and Pd precursors at a certain temperature in ethylene glycol with silver nitrate as structure-controlling agent. The Pt nanoparticles exhibited well-shaped polyhedral morphology with highly fine and specific nanostructures in the size range of 20 nm. Important evidences of core-shell configurations of the Pt-Pd core-shell nanoparticles were clearly characterized by high-resolution transmission electron microscopy (HRTEM) measurements. The results of HRTEM images showed that the core-shell Pt-Pd nanoparticles in the size range of 25 nm with polyhedral morphology were synthesized with the thin Pd shells of ∼3 nm in thickness as the atomic Pd layers grown on the Pt cores. Very interesting characteristics of surface structure of Pt nanostructures and Pt-Pd core-shell nanostructures with surface defects were observed. The high-resolution TEM images of Pt-Pd bimetallic nanoparticles showed that the Frank-van der Merwe and Stranski-Krastanov growth modes coexist in the nucleation and growth of the Pd shells on the as-prepared Pt cores. It is predicted that the FM growth becomes the main favorable growth compared with the SK growth in the formation of the thin Pd shells of Pt-Pd core-shell nanoparticles. The experimental evidence of the deformations of lattice fringes and lattice-fringe patterns was found in Pt and Pt-Pd core-shell nanoparticles. The interesting renucleation and recrystallization at the attachments between the nanoparticles are revealed to form a good lattice match. In addition, our novel ideas of the largest surface-area superlattices and promising utilization of them are proposed for next generations of various fuel cells with low cost. Finally, the products of Pt-Pd core-shell nanoparticles can be potentially utilized as highly efficient catalysts in the realization of polymer electrolyte membrane fuel cell and direct methanol fuel cell using the very low Pt loading with better cost-effective design.

DOI： 10.1021/jp303117y

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The thermoelectric properties of double perovskite-type oxides Ca ₂FeMoO ₆ are investigated in terms of Sr substitution at the A site of the oxides. The electrical conductivity, σ, of Ca _2-xSr _xFeMoO ₆ (0 ≤ x ≤ 0.3) showed a metallic behavior, decreasing monotonically from ca. 10 ³ S cm ^-1 at room temperature to ca. 10 ² S cm ^-1 at 1250 K. At room temperature, although the σ values of the oxides increased with increasing substitution level, x, the σ values maintained almost the same values at high temperature range of 1000-1250 K. The absolute values of the Seebeck coefficient, S, for the samples at x < 0.3 abruptly increase at around 1000 K. The Rietveld refinement of the XRD patterns of the oxides indicated that the anti-site defects in the oxides decreased with increasing Sr concentration. The power factor, S ²σ, of the oxides largely increased with increasing temperature; the S ²σ value of Ca ₂FeMoO ₆ was ca. 0.35 mW mK ^-2 at 1200 K, the largest value of all the samples in this study. Although the thermal conductivity, κ, of the oxides generally decreased from ca. 3.5 to 4.5 W mK ^-1 at room temperature to ca. 2-3 W mK ^-1 at 1050 K, the sample at x = 0.3 showed the lowest and most T-independent κ values, implying that the relative increase in the temperature is independent from the phonon-impurity scattering caused by the A-site substitution. The power factor of the oxides increased above 900 K; thereby, the dimensionless figure of merit, ZT = (S ²σ/κ)T, significantly increased at the same temperature range. The largest ZT value of 0.15 was observed for Ca ₂FeMoO ₆, Ca _1.9Sr _0.1FeMoO ₆, and Ca _1.8Sr _0.2FeMoO ₆ at 1250 K.

DOI： 10.1016/j.matchemphys.2012.01.032

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Pt nanoparticles (NPs) were synthesised by a modified polyol method with the addition of silver nitrate. The results showed that the specific shapes of Pt NPs were influenced by the relevant factors, which are the contents of silver nitrate, synthetic time and temperature. A small content of silver nitrate has played an important role in determining their final shapes of platinum NPs. We observed that Pt NPs in the forms of very sharp shapes such as Pt cubes, octahedrons, cuboctahedrons and tetrahedrons have been obtained. In addition, the shape growth mechanisms and formation of Pt NPs have been studied. They exist in both cubic and octahedral shapes. Importantly, Pt nanocrystals can grow into main cubic and octahedral shapes for a short time less than 15 min. Moreover, Pt nanocrystals can also grow into different shapes from cubic and octahedral into spherical ones for several hours. Especially, they exhibited interesting shapes of multiple-branched Pt nanostructures because of their overgrowth and aggregations. Clearly, large cubic and octahedral Pt NPs of 160 nm diameter were observed. The growth and formation of large cubic and octahedral Pt NPs were due to the aggregation of Pt clusters or initial Pt seeds, even small Pt nanocrystals.

DOI： 10.1080/17458080.2010.513017

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this paper, Pt nanoparticles were successfully prepared by modified polyol method silver nitrate as an effective structure-modifying agent. The characterization of Pt nanoparticles was investigated by using UV-Vis-NIR spectroscopy, transmission electron microscopy (TEM) and high resolution (HR) TEM, and x-ray diffraction (XRD). The method of selected area electron diffraction (SEAD) was used to study the structure of Pt nanoparticles. The results showed that the as-prepared Pt nanoparticles exhibiting the complexity of surface structure and morphology could be used as efficient catalysts for polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs).

DOI： 10.1088/2043-6262/3/2/025005

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The thermoelectric properties of the double perovskite-type oxides Sr _2-xKxFeMoO₆ were investigated in terms of K-doping at the A site of the oxides. The electrical conductivity, of the oxides showed a metallic behavior, decreasing monotonically from ca. 10³ S/cm at room temperature to ca. 10² S/cm at 1250 K. The Seebeck coefficient, S, showed that the oxides are of n-type over the measured temperature range. The absolute value of S increased with increasing temperature. The absolute value of S at 300K increased up to x = 0.2 and then decreased dramatically for x = 0.304. The Rietveld refinement of the XRD patterns of the oxides suggested that the increase in orbital degeneracy due to the eased distortion of FeO ₆ and MoO₆ octahedra at x = 0.2 was responsible for the S maximum at this composition. The power factor, S², of the oxides increased sharply with increasing K-doping level; the value for Sr _1.6K_0.4FeMoO₆ was ca. 4.2 × 10 ^-4W/mK², which is the highest among all the samples in this study. The thermal conductivity, of the oxides generally decreased from ca. 35W/ mK at room temperature to ca. 24W/ mK at 1100 K. Because the power factor of the oxides increased above 900 K, the dimensionless figure of merit, ZT = S²T/, increased dramatically above 900 K. The largest ZT value of 0.24 was observed for Sr_1.6K_0.4FeMoO₆ at 1250 K.

DOI： 10.2109/jcersj2.120.211

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Rapid progress in thermoelectric performance of oxide materials has been conducted virtually exclusively in Japan, resulting in more than 10 times increase in the ZT values of oxides within the last two decades. This has caused a revolutionary change in the guiding principles of thermoelectric materials research, in which oxide materials had been disregarded as a potential candidate until early 1990s. Promising oxide thermoelectric materials having been discovered include CaMnO₃-based perovskites, Al-doped ZnO, layered cobalt oxides represented by NaCo₂O₄ and Ca ₃Co₄O₉, and SrTiO₃-related phases. This paper reviews the current aspects of oxide thermoelectric materials, and some strategies of nanostructure control for selective reduction of the lattice thermal conductivity (selective phonon scattering) in bulk oxide ceramics will also be discussed.

DOI： 10.2109/jcersj2.119.770

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Thermoelectric properties of Al-doped ZnO (Zn_0.98Al _0.02O) with nanosized pore (nanovoid) structure were investigated. Nanovoids were formed by using monodisperse polymethylmethacrylate (PMMA) particles of 150, 425, and 1800nm in average diameter as a void forming agent (VFA). Whereas the thermal conductivity of the samples sintered with the 150nm PMMA particles of 510 wt% was efficiently suppressed, the magnitude of the suppression was almost the same as that of the electrical conductivity, revealing that the selective phonon scattering was failed in these samples. However, being helped by the contribution from an enhancement in the Seebeck coefficient, the samples sintered with 510 wt% of 150nm VFA successfully attained the ZT values of 0.55-0.57 at 1000°C. Furthermore, the reduction of the thermal conductivity with increasing porosity was much steeper than ordinary porous materials, suggesting significantly stronger phonon scattering by the nanosized pore structure.

DOI： 10.2109/jcersj2.119.813

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this article, polyhedral and non-polyhedral Pt nanoparticles were prepared by modified polyol method using AgNO₃ as a good structure-modifying agent. Their TEM and HRTEM images showed the particle size in the range of 8-16 nm for both the above cases. The structures and properties of the surfaces of Pt nanoparticles were investigated through cyclic voltammetry in dilute perchloric acid (HClO₄) electrolyte solution. A comparison of the electrocatalytic property in methanol electrooxidation was made. Here, the effects of polyhedral and non-polyhedral morphologies on their catalytic properties were studied. The results revealed that the special catalytic activity of quasi-sphere non-polyhedral Pt nanoparticles is higher than that of polyhedral Pt nanoparticles. In addition, Pt nanoparticles of un-sharp and quasi-sphere morphologies exhibit the tolerance to poisoning species better than that of Pt nanoparticles of sharp and polyhedral morphologies due to the various morphologies of the catalyst surfaces in the chronoamperometric plots. Therefore, these experimental evidences showed the morphology-dependent catalytic property according to the various morphologies and complexity of their catalyst surfaces.

DOI： 10.1007/s11051-011-0503-z

記述言語：英語   掲載種別：研究論文（学術雑誌）  

This comparative study characterizes two types of metallic and core-shell bimetallic nanoparticles prepared with our modified polyol method. These nanoparticles consist of Pt and Pt-Pd core-shell nanocatalysts exhibiting polyhedral morphologies. The controlled syntheses of Pt metallic nanoparticles in the 10-nm regime (4-8 nm) and Pt-Pd bimetallic core-shell nanoparticles in the 30-nm regime (15-25 nm) are presented. To realize our ultimate research goals for proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs), we thoroughly investigate the dependence of the electrocatalytic properties of the nanoparticles on the structure, size and morphology. Significant differences in the electrocatalysis are also explained in experimental evidences of both Pt and Pt-Pd nanocatalysts. We suggested that the core-shell controlled morphologies and nanostructures of the Pd nanoshell as the Pd atomic monolayers will not only play an important role in producing inexpensive, novel Pt- and Pd-based nanocatalysts but also in designing more efficient Pt- and Pd-based nanocatalysts for practical use in DMFC technology. Our comparative results show that Pt-Pd nanocatalysts with Pd nanoshells exhibited much better electrocatalytic activity and stabilization compared to Pt nanocatalysts. Interestingly, we found that the size effect is not as strong as the nanostructuring effect on the catalytic properties of the researched nanoparticles. A nanostructure effect of the core-shell bimetallic nanoparticles was identified.

DOI： 10.1016/j.electacta.2011.07.090

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this paper, the polyhedral Pt nanoparticles under control were prepared by polyol method using AgNO₃ and poly(vinylpyrrolidone) (PVP) in the reduction of H₂PtCl₆ with ethylene glycol (EG). Transmission electron microscopy (TEM) and high resolution (HR) TEM measurements were used to investigate their characterization. In the case of the previous removal of PVP by washing and heating at 300°C, the specific morphologies of polyhedral Pt nanoparticles were still observed. However, the removal of PVP only by heat treatment at 300°C without washing causes the significant variation of their morphology. The large Pt particles were observed in the self-aggregation and assembly of the as-prepared polyhedral Pt nanoparticles. The pure Pt nanoparticles by washing and heat treatment showed the electrocatalytic property better than PVP-Pt nanoparticles by heat treatment due to the incomplete removal of PVP and by-products from AgNO₃. Therefore, the removal modes of PVP without changing their characterization are required to obtain the good catalytic performance.

DOI： 10.1007/s00396-011-2460-6

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The thermoelectric properties of double-perovskite oxide Sr _2-xLa _xCoTiO _6-δ were revealed to vary anomalously with the La concentration, plausibly due to a structural transition found in this study. Although the temperature dependence of the resistivity and thermopower of the present oxide showed a semiconductor-to-metal transition similar to those observed for other perovskite-related Co oxides such as Sr _1-xY _xCoO _3-δ, the transition temperature was more than 350 K higher, implying considerable stabilization of the low-spin state of Co ions in the double-perovskite oxide. Consequently, the operating temperature range of the oxide for potential thermoelectric applications was significantly expanded toward higher temperatures.

DOI： 10.1063/1.3623476

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In the present research, Pt-Pd core-shell nanoparticles based on the as-prepared and defined Pt-seed cores with well-controlled size and morphology were synthesized. Their characterizations were investigated by using UV-vis spectroscopy, transmission electron microscopy (TEM), and high resolution (HR)TEM measurements. The high resolution elemental mappings were performed in the operation of high angle annular dark field (HAADF) in conjunction with scanning (S)TEM mode and X-ray energy dispersive spectroscopy (XEDS). It is found that not only the Pt-Pd core-shell nanoparticles were formed, but also the nucleation, growth, and the separate formation of single Pd nanoparticles as well. Interestingly, the as-prepared Pt cores without the morphological changes were protected by the overgrowths of the Pd shells during the successive reduction of sodium tetrachloropalladate (II) hydrate. There were the co-existence of the Frank-van der Merwe (FM) layer-by-layer and Stranski-Krastanov (SK) island-on-wetting-layer growth modes of the Pd shells on the as-prepared Pt cores. It is predicted that the SK growth became the favorable growth mode in the formation of the Pd shells in the formation Pt-Pd core-shell nanoparticles.

DOI： 10.1016/j.jallcom.2011.04.031

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In our research, we present the controlled synthesis of poly(vinylpyrrolidone) (PVP) protected Pt-Pd nanoparticles of various alloy and core-shell morphologies by modified polyol method with the assistance of AgNO₃. The Pt-Pd alloy and core-shell nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution TEM, and electrochemical measurements. The comparison of electrocatalytic properties of Pd-Pt bimetallic nanoparticles was described to confirm their highest catalytic performance. Importantly, the catalytic activity of Pt-Pd alloy and core-shell nanoparticles was investigated to develop novel electrocatalysts in direct methanol fuel cells (DMFCs). The results showed that the core-shell nanoparticles with the thin nanoshells as monolayers exhibit as great nanocatalysts. The correlation among structure, size and morphology was presented in their catalytic characterization.

DOI： 10.1016/j.ijhydene.2011.03.140

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this paper, we presented the preparation procedure of Pt nanoparticles with the well-controlled polyhedral morphology and size by a modified polyol method using AgNO₃ in accordance with the reduction of H₂PtCl₆ in EG at high temperature around 160°C. The methods of UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution (HR) TEM measurements were used to characterize their surface morphology, size, and crystal structure. We have observed that the polyhedral Pt nanoparticles of sharp edges and corners were produced in the preferential homogenous growth as well as the formation of porous and large Pt particles by self-aggregation and assembly originating from as-prepared polyhedral Pt nanoparticles. It is most impressive to find that the arrangement of Pt nanoparticles was observed in their surface attachments, self-aggregation, random and directed surface self-assembly by the bottom-up approach. Their high electrocatalytic activity for methanol oxidation was predicted. The findings and results showed that the polyhedral Pt nanoparticle-based catalysts exhibited the high electrocatalytic activity for their potential applications in developing the efficient Pt-based catalysts for direct methanol fuel cells.

DOI： 10.1016/j.jcis.2011.03.029

記述言語：英語   掲載種別：研究論文（学術雑誌）  

An effective way to improve the thermoelectric performance (ZT) of layered structured oxide materials by carefully choosing heavy ion doping and introducing metallic nanoinclusions is proposed. A p-type oxide material with remarkable highly improved ZT is successfully fabricated using this approach. Long-term durability at high temperature testing confirms this material is a very promising p-type material for high temperature power generation.

DOI： 10.1002/adma.201004782

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The effects of Ga substitution on the Co-site on the high-temperature thermoelectric properties and microstructure are investigated for the misfitlayered Ca ₃Co ₄O ₉ and the complex perovskite-related Sr ₃RECo ₄O _10.5 (RE = rare earth) cobalt-based oxides. For both systems, substitution of Ga for Co results in a simultaneous increase in the Seebeck coefficient (S) and the electrical conductivity (σ), and the influence is more significant in the high temperature region. The power factor (S ² σ) is thereby remarkably improved by Ga substitution, particularly at high temperatures. Texture factor calculations using x-ray diffraction pattern data for pressed and powder samples reveal that the Ga-doped samples are highly textured. Microstructure observed by scanning electron microscopy shows very well-crystallized grains for the samples with Ga substitution for Co. Among the Ga-doped samples, Ca ₃Co _3.95Ga _0.05O ₉ shows the best ZT value of 0.45 at 1200 K, which is about 87.5% higher than the nondoped one, a considerable improvement.

DOI： 10.1007/s11664-011-1524-1

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report the preparation of poly(vinylpyrrolidone) (PVP)-protected Rh nanoparticles by modified polyol method with the reduction of RhCl₃ in ethylene glycol at 160 °C using AgNO₃. This method is used to synthesize highly cubic and octahedral Rh nanoparticles with their well-controlled size ∼714 nm characterized by transmission electron microscopy (TEM). At a low AgNO₃ concentration, the appearance of the sharply good morphology of Rh nanoparticles due to their controlled growth of {1 0 0} and {1 1 1} selective surfaces for ∼1015 min is observed. Their morphology between cubic and octahedral shape exhibits their competitive growth along the [1 1 1] and [1 0 0] directions. Interestingly, sharply and highly branched Rh nanoparticles with their shapes of very sharp corners or sharp-tip arms growing in the [1 1 1] directions are synthesized for ∼30 min at the same concentration of RhCl₃ and AgNO₃ precursors. However, at a higher concentration of AgNO₃, the assemblies of Rh multipods leading to large porous Rh nanoparticles are observed. The problems of reaction time and temperature are discussed to clarify the nucleation and growth of Rh nanoparticles. In addition, monolayers of Rh nanoparticles on SERS substrates using a probe as malachite green (MG) molecule exhibit the high sensitivity for their potential applications in chemical and biochemical sensing.

DOI： 10.1016/j.jcrysgro.2011.02.006

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Misfit-layered oxides Ca_3-xLn_xCo₄O _9+δ with Ln = Dy, Er, Ho, and Lu were synthesized using solid state reactions. The resulting samples were hot-pressed (HP) at 1123 K in air for 2 h under a uniaxial pressure of 60 MPa. Thermoelectric properties of Ca_3-xLn_xCo₄O_9+δ were investigated up to 1200 K. Both the Seebeck coefficient and electrical resistivity increase upon Ln substitution for Ca. Among the Ln-doped samples, the magnitude of Seebeck coefficient tends to increase with decreasing ionic radius of Ln³⁺. The Ln-doped samples exhibit a lower thermal conductivity than the non-doped one due to a decrease of their lattice thermal conductivity. The dimensionless figure of merit, ZT, reaches 0.36 at 1073 K for the Ca_2.8Lu_0.2Co₄O_9+δ sample, which is about 1.6 times larger than that for the non-doped counterpart.

DOI： 10.1016/j.jallcom.2010.09.150

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

Oxide thermoelectric materials for heat-to-electricity direct energy conversion

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Highly densified Ca₃Co_4-xGa_xO_9+δ (0 ≤ x ≤ 0.2) misfit-layered thermoelectric oxides are prepared by solid state reaction methods followed by hot-pressing. Thermoelectric properties of the samples are measured from room temperature to 1200 K. The results show that partial Ga substitution leads to a simultaneous increase of the electrical conductivity and thermopower. The Ga-doped samples have lower thermal conductivity than that of the non-doped sample in the high temperature region (>600 K). The x = 0.05 sample shows a higher figure of merit (Z = 3.37 × 10^-4 K^-1) than that of the non-doped sample (Z = 1.98 × 10^-4 K^-1) at 1073 K, indicating significant improvement of the thermoelectric performance of Ca₃Co₄O_9+δ by partial Ga substitution for Co.

DOI： 10.1016/j.jallcom.2009.11.009

記述言語：英語   掲載種別：研究論文（学術雑誌）  

This work presents the results of the successful preparation of Pd nanoparticles by the polyol method and the proposed techniques of controlling their size and shape. Polyvinylpyrrolidone (PVP) stabilized Pd nanoparticles of various shapes with the largest sizes in the forms of octahedrons (24 nm), tetrahedrons (22 nm) and cubes (20 nm) have been obtained by alcohol reduction in ethanol with the addition of a hydrochloric acid catalyst. Moreover, PVP-Pd nanoparticles of well-controlled spherical shapes have also been prepared by a modified polyol method. PVP-Pd nanoparticles of cubic, octahedral, tetrahedral and spherical shapes with well-controlled size achieved by using ethylene glycol (EG) as reductant and various inorganic species were also fabricated. In particular, Pd nanorods with sizes of 47 nm and 16 nm formed due to the anisotropic growth mechanism of Pd nanoparticles were found. At the same time, tetrahedral particles of sharp shapes of 120 nm and 70 nm sizes have been observed. A high concentration of inorganic species was used to control the size and shape of the Pd nanoparticles, leading to the appearance of various irregular sizes and shapes. There was evidence of the very sharp corners and edges of tetrahedral and octahedral Pd nanoparticles or others that were formed in the clustering and combination of the seeds of smaller particles.

DOI： 10.1088/2043-6262/1/3/035012

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A marked improvement in the thermoelectric performance of dense ZnO ceramics is achieved by employing a third element as a co-dopant with Al. Dual doping of ZnO with Al and Ga results in a drastic decrease in the thermal conductivity of the oxide, while the decrease in the electrical conductivity is relatively small. With the aid of a significant enhancement in the thermopower, the dually doped oxide shows thermoelectric figure of merit values, ZT, values of 0.47 at 1000 K and 0.65 at 1247 K at the composition Zn _0.96Al _0.02Ga _0.02O. These results appear to be the highest ZT values so far reported for bulk n-type oxides. Microscopic observation of the samples reveals a granular texture in the densely sintered oxide matrix, suggesting that considerable reduction of the thermal conductivity while maintaining high electrical conductivity could be achieved by such a bulk nanocomposite structure in the samples.

DOI： 10.1007/s11664-009-0816-1

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Doping effects for the A-site in double-perovskite type oxide Sr _2-xM_xFeMoO₆ (M = Ba, La) are investigated on the thermoelectric properties of the oxides. The Seebeck coefficient, S, shows that all the samples of both Ba- and La-doped Sr₂FeMoO₆ systems are n-type over the measured temperature range. In particular, the power factor, S² σ, of the Sr₂FeMoO₆ system largely increased with increasing Ba doping level up to x = 0.3. As a consequence, S² σ of Sr_1.7 Bao _0.3FeMoO₆ reached ca. 0.8 × 10^-4 W/mK², the largest value of all the samples in this study. The thermal conductivity, κ, shows a general trend in which the value decreases from ca. 1 W/mK at room temperature to ca. 0.7 W/mK at 1100 K. The dimensionless figure of merit, ZT, of the Badoped samples increased with increasing Ba doping level. Moreover, the ZT value drastically increased above 700 K due to the S² σ value increasing above 700 K and the κ value decreasing monotonically. As a result, the ZT value of Sr _1.7Ba_0.3FeMoO₆ reached 0.31 at 1100 K.

DOI： 10.2109/jcersj2.116.1278

記述言語：日本語   掲載種別：研究論文（大学，研究機関等紀要）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

Thermoelectric Properties of Double-perovskite Oxide A2 B'MoO6 with A-site Substitution

DOI： 10.15017/14598

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

This article has no abstract.

DOI： 10.1541/ieejjournal.128.293

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

A practical oxide thermoelectric module consisting of 12 pairs of p-NaCo₂O₄ and nanostructured n-ZnO sintered materials was successfully fabricated by using a diffusion welding technique. By applying a nanostructure using a void forming agency (VFA), the electrical conductivity of the n-ZnO sintered materials were drastically enhanced, leading that the power factor of the materials were dramatically improved. It is revealed that the oxide module can be operated up to 930 K on the hot side temperature. A maximum power output of 52.5 mW was achieved at the temperature condition of T _H/T_L = 934/479 K, where T_H and T_L are temperatures at the hot and cold sides of the module, respectively. The details of the power generation characteristics of the present oxide module will be presented and the performance will be discussed with those of our previous and other oxide modules.

DOI： 10.1109/ICT.2007.4569418

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Investigated in this paper is influence of the size and amount of combustible nanosized particles added as a void forming agent (VFA) for generating isolated closed pores (nanovoids) within a densely sintered Al-doped ZnO matrix on the thermoelectric properties of the oxide. With increasing amount of VFA, the electrical conductivity (σ) and the thermal conductivity (κ) of the samples decrease, while the Seebeck coefficient (S) is relatively insensitive to the amount of VFA; these results appear to be a natural consequence concerning increasing porosity. However, conventional κ-porosity relation is revealed to be unapplicable to the present system, showing a much steeper decrease in κ with increasing porosity. These results suggest that the nanovoid structure is capable of scattering phonons more effectively compared to conventional porous structures with similar porosity. Moreover, the S values significantly increase with decreasing average diameter of VFA from 1800 nm down to 150 nm. Consequently, the samples prepared with 5-10wt% of 150 nm VFA show ZT = 0.54 - 0.59 at 1000°C. Detailed investigation of the transport properties of the samples reveals that the &sigma/κ ratios can be larger for the nanoviod samples than that of the dense matrix without VFA, implying a possible selective phonon scattering.

DOI： 10.1109/ICT.2007.4569436

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Highly dispersed nanosized closed pores (nanoviods) are revealed to be effective to substantially enhance the thermoelectric performance of bulk sintered body of n-type Al-doped ZnO oxide, resulting in a dimensionless figure-of-merit of ZT - 0.65 at 1250 K. The nanovoid structure is built in a densely sintered Al-doped ZnO matrix by using combustible nanosized polymer particles as a void forming agent (VFA), the uniformity of the WA distribution in the sintering mixture being greatly improved by employing planetary-type ball milling with high pulverizing capability. A combination of shortened mixing period and liquid mixing media enables us to prevent formation of oxygen-related defects in ZnO, and sintered samples thus obtained show the electrical conductivity (σ) higher than that of those prepared with conventional ball milling. The sintered samples obtained in the present study also show the Seebeck coefficient (S). considerably larger than that of the control sample over the whole temperature range from 300 K to 1273 K, implying an enhancement of the thermopower possibly due to a carrier energy filtering effect by low-energy nanosized defects. Although a decrease in the thermal conductivity (κ) is only of the same magnitude to that of the σ values, the marked increase in both σ and S gives rise to a significant enhancement of the power factor. With fairly suppressed κ values, the nanovoid ZnO samples successfully attain a largest ZT value so far observed for n-type bulk oxide materials.

DOI： 10.1109/ICT.2006.331368

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Thermoelectric properties of a series of rare earth metaldoped polycrystalline samples of (Ca_1-xR_x)₃Co ₂O₆ with R = Gd, Tb, Dy and Ho (x = 0 - 0.1) were investigated in the temperature range from 300 K to 1300 K. In a high temperature region above 900 K, a partial rare earth substitution with R ³⁺ for Ca²⁺ resulted in appreciable increase in the Seebeck coefficient (S). However, the S value decreased abruptly at low temperatures, and turned to negative values for the Gd- and Tb-doped samples at temperatures below 400 K. With decreasing ionic radii of rare earth elements (Gd³⁺ > Tb³⁺ > Dy³⁺ > Ho ³⁺), the S values increased, while the thermal conductivity (Κ) decreased particularly at temperatures above 700 K. Contrastingly, the influence of rare earth metal substitution on the electrical resistiivity (p) was small; in high temperature region the p values increased only slightly with decreasing ionic radii of rare earth metals. High-temperature thermoelectric figure-of-merit (Z) of the samples was thereby improved by the late rare-earth metal substitution for Ca²⁺, particularly for those with Ho ³⁺. A maximum Z value of the Ho-doped sample for x = 0.03 was 1.83×10^-4 K^-1 at 1100 K as compared with 0.37×10^-4 K^-1 for non-doped sample. The electronic structure of the samples was also investigated by x-ray photoemission spectroscopy (XPS) technique. The charge-transfer satellite structure of Co 2p core-level spectra was observed for the Gdand Tb-doped samples, while the satellite is negligible for the other samples.

DOI： 10.1109/ICT.2006.331270

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

A series of seven bulk crystals of Zn_4+xSb₃ (-0.12 ≤ x ≤ 0.12) are successfully prepared, and the relation between the Zn content and the thermoelectric properties is investigated. The sample with the nominal composition of Zn_3.96Sb₃ (x = -0.04) contain the maximum mass fraction of Zn₄Sb₃. The shapes of the S(T) and ρ(T) curves are drastically changed with varying x in the temperature range from 300 K to 700 K. Whereas the lower x leads to lower ρ, the magnitude of S unchanges, resulting in the fact that the power factor of the Zn-poor compositions in the Zn_4+xSb₃ system is lower than that of the Zn-rich compositions. The details of the influence of the Zn content and the scope of the improvement of the durability are discussed.

DOI： 10.1109/ICT.2006.331384

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

CoSb₃ bulk materials were successfully prepared by Sb self-flux technique, and the synthesis conditions were widely investigated to obtain the high purity compounds utilizing a quantitative powder XRD study with the Rietveld analysis applying a multi-phase-fitting condition. The reaction temperature range for the Sb self-flux technique was extended up to 1123 K to promote the reaction in the Co-Sb system. The relation between the reaction temperature and the chemical composition is discussed to optimize the preparation conditions in the Sb self-flux technique.

DOI： 10.1109/ICT.2006.331385

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

A prototype of thermoelectric module using oxide materials has been successfully fabricated, and the power generation characteristics have been examined in the high temperature region around 773 K (500 °C). Twelve couples of sintered p-NaCo₂O₄ and n-ZnO materials were connected via silver conducting strips with a planer arrangement jointed by using a diffusion welding technique under 16 MPa at 1023 K in Ar. A maximum power output of 58 mW was achieved at a temperature condition of T _H/T_L= 839/377 K. The details of the power generation characteristics of the oxide module will be presented and the performance will be discussed with other oxide modules.

DOI： 10.1109/ICT.2006.331386

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（大学，研究機関等紀要）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

A comparison of detailed structural parameters between the 3IS and Mayer models for the Zn_4-xCd_xSb₃ system in the Zn-rich region has been successfully performed by the powder XRD study with the Rietveld method using 9 bulk crystals synthesized by vacuum casting method without annealing. The 3IS model gives a better fitting on the Rietveld analysis not only for the undoped Zn₄Sb₃ but also for the whole compositional range of the Zn-rich region of the Zn_4-xCd _xSb₃ compounds. The purities and densities of the bulk crystals exceeded approximately 96 mass% and 95 % of XRD density, respectively.

DOI： 10.1109/ICT.2005.1519973

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

High purity CoSb₃ bulk crystals have been successfully synthesized by Sb self-flux method and a relation between reaction conditions and chemical composition on the method has been systematically analyzed by powder XRD study using the Rietveld analysis. Sb self flux method at 923 K using 100 mesh Co elements can directly provide a single phase CoSb₃ bulk crystal in a brief time of 10 h. Advantages of Sb self-flux methods will be discussed compared with other preparation methods.

DOI： 10.1109/ICT.2005.1519903

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Influence of gas-solid equilibrium and partial pressures of gaseous species was investigated on solid state reactions of Na₂CO ₃ and Co₃O₄ for synthesis of bulk sintered bodies of layered thermoelectric oxide NaCo₂O₄. It was revealed that the presence of CO₂ in the reaction atmosphere strongly inhibits the formation reaction of NaCo₂O₄. However, precise control of the CO₂ partial pressure in the oxygen atmosphere enabled us to avoid otherwise significant Na loss during sintering at temperature as high as 900°C, thereby allowing high reaction temperature required for incorporation of Na into the crystal lattice. Selective quantification of the Na species in order to distinguish those within the crystallites and at the grain boundaries revealed that the samples synthesized in the presence of dilute CO₂ contain more Na in the crystallites with less Na segregation at the boundaries. Improved interconnection between the grains containing larger amounts of Na was suggested as a reason of higher electrical conductivity and larger Seebeck coefficient of the samples thus obtained, compared to the samples containing the same amount of total Na but synthesized in air.

DOI： 10.1109/ICT.2005.1519988

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Durability of the Zn₄Sb₃ compounds was evaluated in term of their thermoelectric properties by applying repeated heat cycles to the vacuum-casted and hot-pressed samples. The power factor of both samples decreased by applying 20 cycle heat load. The major reason of the deterioration was formation of the ZnCd compounds due to evaporating Zn from the Zn ₄Sb₃ compounds. The degree of the deterioration of the thermoelectric performance and a solution to enhanced durability of the compounds are discussed.

DOI： 10.1109/ICT.2005.1519974

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

Incorporation of Ni ions into two different sites of the Na and Co sites of NaCo₂O₄ was carried out by the processes of conventional elemental substitution for Co ion and solid state ion exchange of mobile Na⁺ ion. The changes of the lattice parameters of "substituted" and "exchanged" samples were different, suggesting that the Ni ions occupy different sites. The Ni-substituted sample for Co showed a significant decrease of Seebeck coefficient keeping the electrical conductivity almost intact, while Ni-exchanged samples for Na showed a lower electrical conductivity than that of the non-substituted sample with keeping the Seebeck coefficient unchanged. These results suggest that Ni cations introduced to the Co site decouples the Co-Co spin exchange, whereas those at the Na site compensates positive holes by providing conduction electrons.

DOI： 10.2109/jcersj.113.400

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Incorporation of Ni ions into two different sites of the Na and Co sites of NaCo₂O₄ was carried out by the processes of conventional elemental substitution for Co ion and solid state ion exchange of mobile Na ⁺ ion. The changes of the lattice parameters of " substituted" and "exchanged" samples were different, suggesting that the Ni ions occupy different sites. The Ni-substituted sample for Co showed a significant decrease of Seebeck coefficient keeping the electrical conductivity almost intact, while Ni-exchanged samples for Na showed a lower electrical conductivity than that of the non-substituted sample with keeping the Seebeck coefficient unchanged. These results suggest that Ni cations introduced to the Co site decouples the Co-Co spin exchange, whereas those at the Na site compensates positive holes by providing conduction electrons.

DOI： 10.2109/jcersj.113.400

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Sintering process of layered oxide NaCo₂O₄, which has been the best p-type thermoelectric oxide candidate to date since its debut in the world of thermoelectrics in 1997, was investigated in terms of sodium nonstoichiometry occurring during solid state reaction between Na₂CO₃ and Co₃O₄ for the synthesis of the oxide. Thermal gravimetry (TG) and differential thermal analysis (DTA) measurements revealed that solid-gas equilibrium plays an important role on phase formation process and on controlling chemical composition of the oxide, Partial pressure of oxygen and carbon dioxide in the reaction atmosphere was revealed to be crucial for controlling vaporization of Na, as well as for promotion of phase formation reaction of NaCo₂O₄, In particular, whereas the CO₂ atmosphere effectively suppressed abrupt dissociation reaction of Na₂CO₃, low oxygen partial pressure accelerated vaporization of Na at lower temperature. Interestingly, high partial pressure Of CO₂ appeared to hinder phase formation reaction of NaCo₂O₄ even at the same oxygen partial pressure as that under the aerobic conditions.

DOI： 10.1109/ICT.2003.1287490

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

The State of the Art of Research and Development in Electroceramics

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Reported are the electrical and thermal transport properties of Al-doped zinc oxide sintered in the presence of void forming agents (VFA) such as small carbon or organic polymer particles of several hundreds nanometers in size. Nanosized cavities (nanovoids) thus formed within dense oxide matrices lead to a marked enhancement in the thermopower, showing a large negative maxima at the temperature range around 400-600°C. On the other hand, the formation of the nanovoids scarcely influences the electrical conductivity, if the size of VFA is sufficiently small. Although the reduction of the thermal conductivity is also fairly small, the enhanced thermopower coupled with the virtually unchanged electrical conductivity results in a considerable improvement in the power factor with the maximum value of 40×10^-4 W/mK², being twice as large as that of the completely dense sample without addition of VFA. The ZT value thereby exceeds 0.4, and the operation temperature range markedly expands toward the lower temperatures. Different behavior of the scattering cross sections for electrons and phonons will be discussed.

DOI： 10.1109/ICT.2003.1287476

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

We have investigated site-selective doping of Ni in order to experimentally explore the roles of the Na and Co sites of NaCO₂O₄. The selective doping is carried out by changing preparation procedures of the oxide. Cation "substitution" is intended by incorporating Ni(NO₃)₂ into a Co-deficient starting mixture of Na₂CO₃ and Co₃O₄ prior to the first heat treatment. Cation "exchange" is, on the other hand, carried out by heating a mixture of Ni(NO₃), and a single phase sample ofNaCo₂O₄, which has been prepared beforehand from a stoichiometric starting mixture. Comparison with control samples without addition of Ni(NO₃)₂ reveals that the "substituted" sample shows a significant decrease in the thermo power with keeping the electrical conductivity almost intact, while the "exchanged" sample shows the lower electrical conductivity with leaving the thermo power unchanged. These results strongly suggest that Ni cations occupy different sites in the Ni-doped samples; disturbing Co-Co spin exchange at the Co site, and compensating holes at the Na site.

DOI： 10.1109/ICT.2002.1190308

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

Research Aspects of Oxide Thermoelectric Materials

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

Oxide semiconductors with MCM-50--like layered structures are synthesized by liquid crystal templating followed by hydrothermal treatment. The band gap energy of hydrothermal-treated lamellar TiO$_2$ shows a substantial blue shift of $Delta E_g=0.31$~eV. The thickness of the 2-dimensional TiO$_2$ sheets estimated from $Delta E_g$ by using Blus' equation describing the quantum-confinement effect agrees within a factor of 1.5 with that determined from TEM observation. A new photoluminescence peak appears at $ca.$ 380~nm, being in good accordance with the wider band gap energy of the lamellar TiO$_2$. Lamellar Fe$_2$O$_3$ and Bi$_2$O$_3$ show sharp absorption peaks at the lower energy of the absorption edges, suggesting exciton absorption observable at root temperature.

DOI： 10.15017/16613

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Hydrolysis of Ti alkoxide in the presence of inverse micelles containing CdS nanoparticles in their hydrophilic interior results in formation of TiO₂/CdS nanocomposites in which the CdS nanoparticles are embedded in a TiO₂ matrix with a thickness of ≤10 nm at the surface of the particles. The primary hydroxyl groups introduced by 2-mercaptoethanol as a capping agent used for preparation of the CdS nanoparticles are considered to play an important role for successful adhesion and growth of the TiO₂ layer on the CdS surfaces. TEM observation strongly supports formation of semiconductor-in-semiconductor heteronanostructure by compartmentalized hydrolysis of Ti alkoxide within the inverse micelles in which the surface-capped CdS nanoparticles coexist.

DOI： 10.1023/A:1004857419242

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Generation of bulk second-order nonlinearity in silica glass requires higher poling temperature or longer poling time than that of near-surface second-order nonlinearity. The threshold conditions for initiating the bulk second-order nonlinearity are studied on Infrasil fused silica glass. The threshold poling time is strongly dependent on the poling temperature. The near-surface second-order nonlinearity is also studied, especially the dependence of thickness of the nonlinear layer on the poling temperature, poling voltage and poling time. Secondary-ion mass-spectroscopy measurement showed depletion of Na⁺ ions at the anodic surface. We assume there is an ionic wave during poling traveling from the anodic surface to generate the dipolar electric field that induces the near-surface second-order nonlinearity.

DOI： 10.1007/s10043-001-0159-5

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

The thermoelectric properties of sintered bodies of NaCo₂O₄, which is so far the most promising p-type candidate for oxide thermoelectric material, are investigated in terms of their sintering conditions. Double-step sintering, for which single-phase NaCo₂O₄ obtained by calcination and sintering with addition of 10% excess of Na each time is re-ground and sintered again, is revealed to attain a marked improvement in the thermoelectric performance of the oxide. The improvement is due to increase in both Seebeck coefficient and electrical conductivity, and is attributed to a distinct enhancement of the two-dimensionality in the crystallites constituting the sintered body. The oxide sintered body consequently attains the figure-of-merit of 0.88×10^-3K^-1 at 600°C, and the maximum ZT of 0.78 at 800°C.

DOI： 10.2497/jjspm.47.1159

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The thermoelectric properties of sintered bodies of NaCo₂O₄, which is so far the most promising p-type candidate for oxide thermoelectric material, are investigated in terms of their sintering conditions. Double-step sintering, for which single-phase NaCo₂O₄ obtained by calcination and sintering with addition of 10% excess of Na each time is re-ground and sintered again, is revealed to attain a marked improvement in the thermoelectric performance of the oxide. The improvement is due to increase in both Seebeck coefficient and electrical conductivity, and is attributed to a distinct enhancement of the two-dimensionality in the crystallites constituting the sintered body. The oxide sintered body consequently attains the figure-of-merit of 0.88×10^-3 K^-1 at 600 °C, and the maximum ZT of 0.78 at 800 °C.

DOI： 10.2497/jjspm.47.1159

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Investigation on oxidative mineralization of various surfactants over TiO₂ photocatalyst reveals an anomalously retarded degradation of the trimethylammonium moiety in cationic surfactants. Model reactions using tetraalkylammonium chlorides as substrates confirm that the stepwise behavior of the mineralization time courses is ascribed to intramolecularly selective decomposition caused by a considerably slow degradation rate of the methyl groups directly bound to the quaternary nitrogen. A strong inhibition effect of bromide or iodide anions preventing the complete mineralization is also revealed.

DOI： 10.1016/S1381-1169(99)00325-8

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Promising p-type thermoelectric properties of a layered transition metal oxide Na_xCoO₂ are discussed in terms of crystal chemistry and the conduction mechanism. Highly anisotropic spatial distribution of 3d orbitals coupled with an unusually short Co-Co interatomic distance in the ab plane, along which edge-sharing CoO₆ octahedra connecting each other to form the CoO₂ sheets, strongly suggest that Co3d dε-dε (t_2g-t_2g) direct overlapping is plausible for establishing hole conduction in the valence band with a fairly covalent character. An extremely low thermal conductivity (≤1 W/mK) of the oxide is also revealed, implying contribution of the randomly distributed Na vacancies and an inherent advantage of materials with low-dimensional crystal structure. In spite of insufficient densification, sintered bodies fired under atmospheric pressure shows ZT≈0.5. Possible influence of the ionic conduction of Na⁺ on the thermoelectric properties of the oxide is also examined.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Thermoelectric properties of Chevrel-type sulfides AMo_6S_8 (A=Fe, Ni, Ag, Zn, Sn, Pb, Cu) were investigated with respect to many advantageous characteristics of the Chevrel compounds for thermoelectric applications. The electrical conductivity, σ, was 10^2.5S・cm^<-1><10^3S・cm^<-1> for most of the samples from room temporature to 1000℃; AgMo_6S_8 gave the largest σ up to 250℃. The Seebeck coefficient, S, was positive for all the samples, indicating the p-type conduction. All the S values were 10μV・K^<-1><S<80μV・K^<-1>and AgMo_6S_8 showed smallest S, probably owing to the higher hole concentration for A=Ag compared to other samples. The maximum S^2σ value was attained by SnMo_6S_8, reaching ca. 1.7×10^<-4> W・m^<-1.>K^<-2> at 800℃. All the k values were 1 W・m^<-1.>K^<-1><κ<3W・m^<-1.>K^<-1> from room temperature to 1000℃. The maximum Z value was ca. 0.07×10^<-3>K^<-1> attained by SnMo_6S_8 at 800℃.

DOI： 10.2109/jcersj.107.697

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Thermoelectric properties of Chevrel-type sulfides AMo₆S₈ (A=Fe, Ni, Ag, Zn, Sn, Pb, Cu) were investigated with respect to many advantageous characteristics of the Chevrel compounds for thermoelectric applications. The electrical conductivity, σ, was 10^2.5 S·cm^-1<σ<10³ S·cm^-1 for most of the samples from room temperature to 1000°C; AgMo₆S₈ gave the largest σ up to 250°C. The Seebeck coefficient, S, was positive for all the samples, indicating the p-type conduction. All the S values were 10 μV·K^-1<S<80 μV· K^-1, and AgMo₆S₈ showed the smallest S, probably owing to the higher hole concentration for A=Ag compared to other samples. The maximum S²σ value was attained by SnMo₆S₈, reaching ca. 1.7 × 10^-4 W·m^-1· K^-2 at 800°C. All the κ values were 1 W·m^-1·K^-1<κ<3 W·m^-1·K^-1 from room temperature to 1000°C. The maximum Z value was ca. 0.07 × 10^-3 K^-1 attained by SnMo₆S₈ at 800°C.

DOI： 10.2109/jcersj.107.697

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/ja980430d

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A semiconductor composite of CdS particles embedded in a TiO₂ gel after heat treatment at 250°C in air is revealed to show catalytic H₂ evolution from an EDTA aqueous solution with light of λ ≤ 450 nm, in contrast to bare CdS which is stoichiometrically photocorroded. A significant improvement in the activity even with considerable loses of CdS in the gel during the heat treatment suggests that the TiO₂ gel crystallized into anatase can prevent photocorrosion of CdS embedded therein, and serve as a semiconducting matrix to facilitate charge transfer from the embedded CdS to Pt at the surfaces of the gel.

DOI： 10.1016/S1381-1169(97)00132-5

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A composite oxide containing samaria-doped eeria [SDC, (CeO₂)_0.8(SmO_1.5)_0.2] and yttria-stabilized zirconia [YSZ, (ZrO₂)_0.92(Y₂O₃)_0.08] was developed as an electrolyte for a solid oxide fuel cell (SOFC). A SOFC with a YSZ electrolyte was characterized by a high open-circuit voltage (OCV) and a steep decrease in voltage, V, with increasing current, I, whereas that with a SDC electrolyte exhibited a low OCV and a gradual decrease of its V-I curve. A biphasic electrolyte microstructure with SDC and YSZ was proposed in which SDC grains are dispersed in a YSZ matrix. In this composite structure, the electronic conduction caused by reduction of the SDC was effectively blocked by the YSZ matrix. An SOFC with this composite electrolyte offered the advantages of YSZ with its high OCV and SDC with its gradual decrease of the V-I curve. The SDC content and the particle size significantly affected the power-generation characteristics of a cell with this composite electrolyte. The electrode polarization was significantly lowered by using the SDC or the composite electrolyte.

DOI： 10.1149/1.1838378

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Oxide semiconductor junctions formed by attaching p- and n-type SrTiO₃ exhibits a markedly nonohmic current-voltage characteristics at the steady state, showing no typical rectifying characters. Although the voltages which appeared immediately after applying the currents, are completely linear vs. the current values, the probe voltages vary with time and finally result in a significantly nonlinear behavior strongly dependent on oxygen partial pressure, showing distinct asymmetry to the current direction. Separation of the voltage drop into those within the bulks and at the junction reveals that the highly resistive p-type SrTiO₃ bulk near the junction is mainly responsible for the nonohmic character. For the p-type SrTiO₃ single bulk, absorption of oxygen in the gas phase is observed on applying large bias currents, regardless of the current directions. However, the junctioned sample desorbs oxygen for the forward bias, while the reverse bias causes oxygen absorption. Conductivity changes of the highly resistive p-type SrTiO₃ as a consequence of these current-induced redox behavior give a consistent explanation for the direction-dependent nonohmic character of the junctioned sample. Dissociation/association of oxygen due to a shift of the solid-gas equilibrium caused by the applied currents is discussed.

DOI： 10.1149/1.1838433

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Addition of MgO to Al-doped ZnO was successful in reduction of the phonon thermal conductivity, κ_ph, in order to suppress the unfavorably high thermal conductivity, κ, of the material in terms of applications to thermoelectric conversion. The electrical conductivity, σ, of Zn_0.98Al_0.02O decreased with increasing amount of the added MgO, whereas the Seebeck coefficient was virtually unchanged up to (Zn_0.9Mg_0.1)_0.98Al_0.02O. Further Al₂O₃ doping was ineffective in improving σ. The carrier mobility decreased with increasing amount of the added MgO but was independent of the extent of the Al doping. In spite of the significant suppression of κ, the figure of merit was smaller for the MgO-added samples because of the marked decrease of σ.

DOI： 10.1039/a706213c

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/cm9801744

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The CO₂ evolution rate for photocatalytic mineralization of alkyltrimethylammonium chloride sharply decreased when the mineralization yield became nearly equal to the proportion of the long alkyl carbon to the total organic carbon, suggesting that the photodecomposition rate of the alkyl chains is much faster than that of the trimethylammonium group. Moreover, the presence of Br^- significantly suppressed the initial CO₂ evolution rate, and resulted in incompleted mineralization with the final mineralization yield virtually equal to the proportion of the carbon atoms not attaching to the quarternary nitrogen.

DOI： 10.1246/cl.1998.251

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Investigation on thermoelectric properties of oxide solid solutions based on Zn_0.98Al_0.02O revealed that the thermal conductivity of Al-doped ZnO was markedly suppressed via formation of solid solution, particularly for those with MgO. The decrease in the thermal conductivity was significant at the lower temperatures, and at room temperature, (Zn_0.9Mg_0.1)_0.98Al_0.02O attained a value less than a quarter of that for Zn_0.98Al_0.02O. However, the electrical conductivity also decreased, while the Seebeck coefficients almost unchanged. The Hall measurements revealed reduction in both the carrier concentration and the Hall mobility for the solid solution samples. In spite of the significant suppression of the thermal conductivity, improvement in the figure of merit was unsuccessful for the MgO-doped samples because of the unfavorable decrease in the electrical conductivity.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1023/A:1018599229805

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The thermoelectric properties of a mixed oxide (Zn_1-xAl_x)O (x = 0, 0.005, 0.01, 0.02, 0.05) are investigated in terms of materials for high-temperature thermoelectric conversion. The electrical conductivity, σ, of the oxide increases on Al-doping by more than three orders of magnitude up to ca. 10³ S cm^-1 at room temperature, showing metallic behaviour. The Seebeck coefficient, S, of (Zn_1-xAl_x)O (x > 0) shows a general trend in which the absolute value increases gradually from ca. -100 μV K^-1 at room temperature to ca. -200 μV K^-1 at 1000°C. As a consequence, the power factor, S²σ, reaches ca. 15 × 10^-4 W m^-1 K^-2, the largest value of all reported oxide materials. The thermal conductivity, κ, of the oxide decreases with increasing temperature, owing to a decrease in the lattice thermal conductivity which is revealed to be dominant in the overall κ. In spite of the considerably large values of κ-, the figure of merit, Z = S²σ/κ, reaches 0.24 × 10^-3 K^-1 for (Zn_0.98Al_0.02)O at 1000°C. The extremely large power factor of (Zn_1-xAl_x)O compared to other metal oxides can be attributed to the high carrier mobility revealed by the Hall measurements, presumably resulting from a relatively covalent character of the Zn-O bond owing to a fairly small difference of the electronegativities of Zn and O. The dimensionless figure of merit, ZT, of 0.30 attained by (Zn_0.98Al_0.02)O at 1000°C demonstrates the potential usefulness of the oxide.

DOI： 10.1039/a602506d

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A mixed oxide (Zn_1-xAl_x)O exhibits promising thermoelectric properties attaining a dimensionless figure of merit ZT of 0.30 at 1000 °C, which value is much superior to other oxides and quite comparable to conventional state-of-the-art thermoelectric materials. The addition of a small amount of Al₂O₃ to ZnO results in a large power factor of 10-15×10^-4 W/mK², showing a marked increase in the electrical conductivity while retaining moderate thermoelectric power. A large product of the carrier mobility and density of states would be responsible for the favorable electrical properties of the present oxide. A figure of merit Z=0.24×10^-3 K^-1 is attained by (Zn^0.98Al_0.02)O at 1000 °C, even with a high thermal conductivity. A predominant proportion of the phonon thermal conductivity promises a further improvement in the thermoelectric performance by selective enhancement of phonon scattering.

DOI： 10.1063/1.360976

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ultrafine platinum particles protected by poly (methyl acrylate-co-N- vinyl-2-pyrrolidone) were applied to the immunological detection of methamphetamine (MA). The polymer-protected ultrafine particles could chemically bind anti-methamphetamine monoclonal antibody to their surfaces. The antibody-fixed particles behaved like an antibody in the immunoreaction. The antibody-bound particles competitively reacted against the immobilized and the free antigens in the ELISA system. MA could be detected down to a concentration of ca. 10 ng/ml. In the immuno-dot assay, 10-100 ng/ml of MA was detected within 30 min using the ultrafine particles.

DOI： 10.1016/0922-338X(96)89164-1

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Nanosized CdS particles of ≤6 nm average diameter are prepared at ambient conditions by use of controlled hydrolysis of P₂S₅ in absolute ethanol initiated by addition of an alcoholic Cd(NO₃)₂·4H₂O solution, resulting in an excitonic absorption peak of the particles at 350 nm corresponding to a LUMO-HOMO gap energy of 3.1 eV.

DOI： 10.1039/cc9960001209

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The electrical transport properties of (Ca_0.9M_0.1)MnO₃(M = Y, La, Ce, Sm, In, Sn, Sb, Pb, Bi) are investigated in terms of a new material for high-temperature thermoelectric conversion. The substitution at the Ca site causes a marked increase in the electrical conductivity σ, along with a moderate decrease in the absolute value of the Seebeck coefficient S. The plots of log σT vs 1/T show a negative linear relation, indicating that hopping conduction occurs in these oxides. The σ values at room temperature increase with increasing ionic radii of the cation substituents, implying an increase in the carrier mobility due to larger intersite distance for hopping. The sample of (Ca_0.9Bi_0.1)MnO₃ attains the largest power factor, 2.8 × 10^-4/W m^-1K^-2, at 800°C and leads to the figure of merit 0.7-0.75 × 10^-4K^-1 over the wide range of temperatures 600-900°C. The oxide shows a maximum ZT value of 0.085 at 900°C.

DOI： 10.1006/jssc.1995.1384

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Surface morphology of MoO₃ was observed with an atomic force microscope. The array of (MoO₆)^6- octahedra was clearly observable for the oxidized surface of a thin crystal prepared by the evaporation-condensation process. Similar high resolution AFM image was also obtained for the powder sample which was coated and dried on the substrate using an ethanol suspension. The high resolution image of the (MoO₆)^6- array disappeared after heating the thin crystal in reducing atmosphere at 350°C, but restored after reoxidation in air at 500°C. Vacuum deposited MoO₃ film on silica glass was amorphous and its surface was smooth and flat after heating at or below 300°C. The film crystallized on heating at 400°C accompanying a slight microstructural change at the film surface. This film exhibited sharp diffraction lines from (0k0) planes. The thin film morphology was destroyed and changed into randomly oriented particles after heating at 500°C.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The immunological properties of ultrafine platinum particles protected with poly(methyl acrylate)-co-N-vinyl-2-pyrrolidone, having a group chemically reactive with protein, were examined. Polymer-protected ultrafine particles were able to chemically bond multiple human serum albumin (HSA) molecules on their surface. The particles behaved as a multiepitope-type antigen for the immunoreaction. In an ELISA, the HSA-bound particles and HSA molecules competitively reacted against the anti-HSA monoclonal antibodies. The limit of detection of HSA was ca. 10 ng/ml in the assay. The particles were used in an immunodot analysis of anti-HSA polyclonal antibody. Within 30 min of the reaction, 110 μg/ml of HSA was detected. The protein fixed polymer-protected ultrafine particles are a useful new material in immunochemistry.

DOI： 10.1006/abio.1994.1176

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The thermoelectric properties of mixed oxides ln₂O₃-MO_x(MO_x=Cr₂O₃, Mn₂O₃, NiO, ZnO, Y₂O₃, Nb₂O₅, SnO₂) are investigated in terms of the thermoelectric materials at high temperature. The Seebeck coefficients, S, of all the samples have negative values, and those of ln₂O₃•SnO₂ and ln₂O₃•ZnO increase linearly with temperature, attaining values of -90 and -210 μV K^-1 at 1000 °C, respectively. The electrical conductivities, σ, of these oxides are significantly high. The power factor S²σ of the oxides has constantly positive temperature coefficients up to over 1000 °C. Rather low thermal conductivities, k, of the sintered bodies of the oxides, ca. 1.7 W m^-1 K^-1 at room temperature, lead to the largest value of the thermoelectric figure of merit Z=0.4 × 10^-4 K^-1 for M = Sn at 1000 °C, and the Z value increases toward higher temperatures.

DOI： 10.1039/JM9940400653

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/0925-4005(93)85062-F

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/BF00729402

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Metal clusters were immobilized on crosslinked polymers by two methods. One is the immobilization of polymer-protected platinum or rhodium clusters by covalent bond formation between the protective polymer and the crosslinked polymer support. The immobilization was attributed to the formation of amide bonds by the reaction of methyl acrylate residues of the protective polymer with amino groups of the aminoethylated polyacrylamide gel. In the other method, palladium clusters were immobilized on chelate resin-metal complexes by reduction of palladium ions supported on the resin complexes which are characterised by high porosity. In this case the chelate resin works as both the support and as the protective polymer of the clusters. Both the immobilized metal clusters preferably catalyzed the hydrogenation of C=C bonds in hydrophilic substrates, in particular the substrate containing a carboxyl group. This substrate selectivity can be explained by the acid-base interaction between the substrate and the polymer support.

DOI： 10.1016/0923-1137(91)90157-J

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ultrafine rhodium particles prepared by alcohol reduction in the presence of a protective polymer were covalently immobilized onto a cross-linked polymer support by forming the amide bond between the primary amino group contained in the support and the methyl acrylate residue in the protective polymer of the particles. Catalytic activity of the immobilized particles was investigated in catalytic hydrogenation of olefins. The activity strongly depended on the substrates used in the reactions. The immobilized ultrafine rhodium particles preferentially hydrogenated hydrophilic substrates. In particular, the substrates containing a carboxyl group were hydrogenated by the immobilized catalyst more easily than by the dispersed catalyst of the ultrafine rhodium particles before the immobilization. The difference in the hydrogenation rates can be correlated with the solubility parameter of the substrates. Electrostatic interaction between the substrates and the polymer support leads to increased reaction rates.

DOI： 10.1021/ma00020a014

担当ページ：「熱電材料としての酸化物」pp. 204-213   記述言語：日本語   著書種別：学術書

担当ページ：第2節, pp. 28-45.   記述言語：日本語   著書種別：学術書

担当ページ：ISBN: 0-8493-2264-2, pp.35-1〜35-15   記述言語：英語   著書種別：学術書

Kunihito KOUMOTO, Ichiro TERASAKI, Tsuyoshi KAJITANI, Michitaka OHTAKI, Ryoji FUNAHASHI Oxide Thermoelectrics in Thermoelectrics Handbook: macro to nano, Ed. D. M. Rowe, CRC Press, Inc., Boca Raton, 2006, chap. 35, 1-15

担当ページ：pp. 163-169   記述言語：日本語   著書種別：学術書

担当ページ：ISBN 81-7736-100-7, pp. 159-180.   記述言語：英語   著書種別：学術書

Oxide Thermoelectric Materials: An Overview with Some Historical and Strategic Perspectives Michitaka OHTAKI in Oxide Thermoelectrics, Ed. K. Koumoto, I. Terasaki, N. Murayama, Research Signpost, Trivandrum, India, 2002, ISBN 81-7736-100-7, pp. 159-180.

担当ページ：Chapter 3, pp. 41-74.   記述言語：英語   著書種別：学術書

担当ページ：6.1節、pp. 111-118   記述言語：日本語   著書種別：学術書

担当ページ：pp. 270-277   記述言語：日本語   著書種別：学術書

担当ページ：pp. 233-237   記述言語：日本語   著書種別：学術書

開催年月日： 2020年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：オンライン   国名：日本国  

開催年月日： 2020年9月

記述言語：日本語  

開催地：オンライン   国名：日本国  

開催年月日： 2020年9月

記述言語：日本語  

開催地：オンライン   国名：日本国  

開催年月日： 2020年9月

記述言語：日本語  

開催地：オンライン   国名：日本国  

開催年月日： 2020年3月

会議種別：口頭発表（一般）  

開催地：デンカ(株)イノベーションセンター   国名：日本国  

開催年月日： 2020年3月

会議種別：口頭発表（招待・特別）  

開催地：明治大学   国名：日本国  

開催年月日： 2019年11月 - 2019年10月

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開催地：沖縄コンベンションセンター   国名：日本国  

A highly regulated superlattice structure consisting of two-dimensional titanium oxide of ca. 1.5 nm in thickness with a d-spacing of 3 - 4 nm was synthesized in an aqueous solution by using bilayer micelles of sodium dodecylphosphate (SDP) surfactant as an organic molecule for a self-assembly template. A powder XRD study revealed that the product showed only (00l) diffractions in the low-2θ region, which are characteristic of a lamellar structure with a d001 spacing of ca. 4 nm. Moreover, hydrothermal (HT) post-treatment at 120 °C in distilled water markedly sharpened the (00l) diffractions, suggesting a substantial improvement in the spatial regularity of the layered structure. Precise temperature control of the solutions during the mixing and aging was revealed to be crucial to obtain highly regulated superlattice-like layered nanostructure. The optical absorption edge of the superlattice samples showed a large blue-shift of compared to that of bulk TiO2, suggesting an electron confinement effect in the titanium oxide layers. Au ions were intercalated by using a phase-transfer catalyst into the hydrophobic interior of the bilayer micelles interleaving the TiO2 layers, and were subsequently reduced to obtain Au nanoparticles. The samples thus prepared showed an absorption peak in the visible light region and exhibited higher photocatalytic activity compared with layered TiO2 without Au as well as commercial TiO2 (P-25). It demonstrated that the Au nanoparticles enhanced the visible light photocatalytic activity of the layered TiO2 with the superlattice structure. Fe-based oxide superlattice with presumably amorphous oxide framework was also biomimetically synthesized with the SDP micelles as the self-assembly template followed by the HT post-treatment (Fig. 1, Sample A). Whereas the low-angle (00l) diffractions disappeared after calcination at 350 °C (Sample B), the calcined samples immersed in an SDP aqueous solution successfully recovered the (00l) diffractions assigned to the superlattice structure (Sample C), indicating that the highly regulated layered structure once collapsed was reconstructed by the SDP molecules. These results also strongly suggest that the two-dimensionality of each oxide layer remained intact even after the calcination. It was also revealed that the bandgap energy of the samples alternatingly and reversibly switches between ca. 3.0 and 3.5 eV with the calcination/reconstruction cycles, implying that the disordering/reordering of the superlattice structure is responsible for the switching of the bandgap energy.

開催年月日： 2019年11月 - 2019年10月

会議種別：口頭発表（一般）  

開催地：沖縄コンベンションセンター   国名：日本国  

開催年月日： 2019年11月 - 2019年10月

記述言語：英語  

開催地：沖縄コンベンションセンター   国名：日本国  

開催年月日： 2019年11月 - 2019年10月

記述言語：英語  

開催地：沖縄コンベンションセンター   国名：日本国  

開催年月日： 2019年11月 - 2019年10月

記述言語：英語  

開催地：沖縄コンベンションセンター   国名：日本国  

開催年月日： 2019年11月

会議種別：口頭発表（一般）  

開催地：鳥取県民文化会館   国名：日本国  

開催年月日： 2019年9月

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開催地：Limassol   国名：キプロス共和国  

開催年月日： 2019年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：名古屋工業大学   国名：日本国  

開催年月日： 2019年9月

記述言語：日本語  

開催地：名古屋工業大学   国名：日本国  

開催年月日： 2019年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：名古屋工業大学   国名：日本国  

開催年月日： 2019年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：名古屋工業大学   国名：日本国  

開催年月日： 2019年8月

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開催地：Cancun   国名：メキシコ合衆国  

開催年月日： 2019年6月 - 2019年7月

記述言語：英語  

開催地：Gyeongju Hwabaek International Convention Center   国名：大韓民国  

開催年月日： 2019年6月 - 2019年7月

記述言語：英語  

開催地：Gyeongju Hwabaek International Convention Center   国名：大韓民国  

開催年月日： 2019年6月 - 2019年7月

記述言語：英語  

開催地：Gyeongju Hwabaek International Convention Center   国名：大韓民国  

開催年月日： 2019年6月 - 2019年7月

記述言語：英語  

開催地：Gyeongju Hwabaek International Convention Center   国名：大韓民国  

開催年月日： 2019年6月 - 2019年7月

記述言語：英語  

開催地：Gyeongju Hwabaek International Convention Center   国名：大韓民国  

開催年月日： 2019年5月

会議種別：口頭発表（一般）  

開催地：Congress & Exhibition Centre Acropolis, Nice   国名：フランス共和国  

Zinc oxide has been one of the most promising n-type thermoelectric oxides with relatively large power factor values competitive to major non-oxide candidates such as skutterudites and clathrate compounds. However, a substantially high lattice thermal conductivity of ZnO has limited its ZT values below 0.7, despite a number of attempts to suppress the thermal conduction in the oxide. Here we report an anomalously large reduction of the lattice thermal conductivity, ph, of ZnO doped with Al and Cu simultaneously. The ZnO samples doped with equimolar amounts (x at. % to Zn) of Al and Cu showed a significant peak shift in their XRD patterns, which has never been observed on single doping of Al or Cu. Moreover, the ph values of the samples at x = 8 was as low as 5 and 1.5 W/Km at room temperature and 800 °C, respectively. By comparing with those of Al-doped ZnO at x = 2, which are 40 and 8 W/Km at the corresponding temperatures, a 80% reduction of ph is overwhelming. A remarkable increase in the occupancy of Al in the 4-fold coordination was clearly confirmed by 27Al MAS solid state NMR, evidencing an extended solubility limit of Al into the Zn site in the presence of Cu as a co-dopant. It should also be noted that the ph value at 800 °C, 1.5 W/Km, is very close to the theoretical lower limit of 1.2 W/Km predicted for ZnO above room temperature.

開催年月日： 2019年4月

会議種別：口頭発表（招待・特別）  

開催地：北九州国際会議場   国名：日本国  

開催年月日： 2019年1月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：Daytona Beach, FL   国名：アメリカ合衆国  

Zinc oxide has been one of the most promising n-type thermoelectric oxides with relatively large power factor competitive to major non-oxide candidates such as skutterudites and clathrate compounds. However, a quite high lattice thermal conductivity of ZnO has limited its ZT values below 0.7, despite a number of attempts to suppress the thermal conduction in the oxide. The ZnO samples doped with equimolar amounts (x at. % to Zn) of Al and Cu showed a significant peak shift in their XRD patterns, which has never been observed on single doping of Al or Ga. Moreover, the thermal conductivity of the samples at x = 8 was as low as 5 and 1.5 W/Km at room temperature and 800 °C, respectively. By comparing with the thermal conductivity of 40 and 8 W/Km for Al-doped ZnO at x = 2 at the corresponding temperatures, a drastic reduction of the thermal conductivity was obvious. An enhanced substitution of Zn with Al was clearly observed by 27Al MAS solid state NMR as enriched Al in the 4-fold coordination, evidencing an extended solubility limit of Al into the ZnO lattice in the presence of Cu as a co-dopant. It should also be noted that the value at 800 °C is very close to the theoretical lower limit of 1.2 W/Km for ZnO above room temperature.

開催年月日： 2018年12月

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開催地：Siem Reap   国名：カンボジア王国  

開催年月日： 2018年11月

会議種別：口頭発表（一般）  

開催地：龍谷大学響都ホール校友会館   国名：日本国  

開催年月日： 2018年9月

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開催地：東北大学青葉山キャンパス   国名：日本国  

開催年月日： 2018年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：東北大学青葉山キャンパス   国名：日本国  

開催年月日： 2018年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：東北大学青葉山キャンパス   国名：日本国  

開催年月日： 2018年9月

記述言語：日本語  

開催地：東北大学青葉山キャンパス   国名：日本国  

開催年月日： 2018年9月

記述言語：日本語  

開催地：東北大学青葉山キャンパス   国名：日本国  

開催年月日： 2018年9月

記述言語：日本語  

開催地：東北大学青葉山キャンパス   国名：日本国  

開催年月日： 2018年9月

記述言語：日本語  

開催地：名古屋工業大学   国名：日本国  

開催年月日： 2018年9月

記述言語：日本語  

開催地：名古屋工業大学   国名：日本国  

開催年月日： 2018年8月

会議種別：口頭発表（一般）  

開催地：Vancouver   国名：カナダ  

開催年月日： 2018年7月

会議種別：口頭発表（一般）  

開催地：Caen   国名：フランス共和国  

開催年月日： 2018年7月

会議種別：口頭発表（一般）  

開催地：Caen   国名：フランス共和国  

開催年月日： 2018年7月

記述言語：英語  

開催地：Caen   国名：フランス共和国  

開催年月日： 2018年6月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Rome   国名：イタリア共和国  

開催年月日： 2018年1月

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開催地：Daytona Beach   国名：アメリカ合衆国  

開催年月日： 2017年11月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Bangkok   国名：タイ王国  

開催年月日： 2017年11月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Phan Thiet   国名：ベトナム社会主義共和国  

開催年月日： 2017年10月 - 2017年11月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：高雄   国名：台湾  

開催年月日： 2017年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：神戸大学鶴甲第一キャンパス   国名：日本国  

開催年月日： 2017年9月

記述言語：日本語  

開催地：大阪大学豊中キャンパス   国名：日本国  

開催年月日： 2017年9月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：物質・材料研究機構（つくば市）   国名：日本国  

開催年月日： 2017年8月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Barcelona   国名：スペイン  

開催年月日： 2017年7月 - 2017年8月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Pasadena   国名：アメリカ合衆国  

開催年月日： 2017年7月 - 2017年8月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Pasadena   国名：アメリカ合衆国  

開催年月日： 2017年7月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Budapest   国名：ハンガリー共和国  

開催年月日： 2017年7月

記述言語：日本語   会議種別：口頭発表（一般）  

国名：日本国  

開催年月日： 2017年5月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Waikoloa, Hawaii   国名：アメリカ合衆国  

開催年月日： 2017年5月

記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

開催地：Ho Chi Minh City   国名：ベトナム社会主義共和国  

開催年月日： 2017年5月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Ho Chi Minh City   国名：ベトナム社会主義共和国  

開催年月日： 2017年3月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：慶應義塾大学日吉キャンパス   国名：日本国  

開催年月日： 2017年2月 - 2017年3月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：San Diego   国名：アメリカ合衆国  

開催年月日： 2016年11月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Daejeon   国名：大韓民国  

開催年月日： 2016年10月

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Dubai   国名：アラブ首長国連邦  

開催年月日： 2016年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：広島大学   国名：日本国  

開催年月日： 2016年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：広島大学   国名：日本国  

開催年月日： 2016年9月

記述言語：日本語  

開催地：東京理科大学葛飾キャンパス（東京都葛飾区）   国名：日本国  

開催年月日： 2016年9月

記述言語：日本語  

開催地：東京理科大学葛飾キャンパス（東京都葛飾区）   国名：日本国  

開催年月日： 2016年4月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Clearwater   国名：アメリカ合衆国  

開催年月日： 2016年3月 - 2016年4月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Phoenix   国名：アメリカ合衆国  

開催年月日： 2016年3月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：早稲田大学西早稲田キャンパス   国名：日本国  

開催年月日： 2016年3月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：早稲田大学西早稲田キャンパス   国名：日本国  

開催年月日： 2016年3月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：早稲田大学西早稲田キャンパス   国名：日本国  

開催年月日： 2016年2月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Orlando   国名：アメリカ合衆国  

開催年月日： 2015年12月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Marrakesh   国名：モロッコ王国  

開催年月日： 2015年11月 - 2015年12月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Boston   国名：アメリカ合衆国  

開催年月日： 2015年11月 - 2015年12月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Boston   国名：アメリカ合衆国  

開催年月日： 2015年10月 - 2015年6月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Jeju   国名：大韓民国  

開催年月日： 2015年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：富山大学   国名：日本国  

開催年月日： 2015年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：富山大学   国名：日本国  

開催年月日： 2015年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：九州大学筑紫キャンパス（福岡県春日市）   国名：日本国  

開催年月日： 2015年9月

記述言語：日本語  

開催地：九州大学筑紫キャンパス（福岡県春日市）   国名：日本国  

開催年月日： 2015年9月

記述言語：日本語  

開催地：九州大学筑紫キャンパス（福岡県春日市）   国名：日本国  

開催年月日： 2015年8月

記述言語：英語  

開催地：Stockholm   国名：スウェーデン王国  

開催年月日： 2015年6月 - 2015年7月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Dresden   国名：ドイツ連邦共和国  

開催年月日： 2015年6月 - 2015年7月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Dresden   国名：ドイツ連邦共和国  

開催年月日： 2015年6月 - 2018年6月

記述言語：英語  

開催地：Vancouver   国名：カナダ  

開催年月日： 2015年5月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Paris   国名：フランス共和国  

開催年月日： 2015年3月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Busan   国名：大韓民国  

開催年月日： 2015年3月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：東京大学駒場キャンパス   国名：日本国  

開催年月日： 2015年1月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Orlando, MI   国名：アメリカ合衆国  

開催年月日： 2014年12月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Bangalore   国名：インド  

開催年月日： 2014年11月 - 2014年12月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Boston, MA   国名：アメリカ合衆国  

開催年月日： 2014年11月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Ho Chi Minh City   国名：ベトナム社会主義共和国  

A highly regulated superlattice structure consisting of two-dimensional titanium oxide of ca. 1.5 nm in thickness with a d-spacing of 3 - 4 nm was synthesized in liquid phase using bilayer micelles of sodium alkylphosphate surfactant as an organic self-assembly template. A powder XRD study revealed that the product showed only (00l) diffractions in the low-2θ region, which are characteristic of a lamellar structure with a d001 spacing of ca. 4 nm. Moreover, hydrothermal (HT) post-treatment at 120 °C in distilled water markedly sharpened the (00l) diffractions, suggesting a substantial improvement in the spatial regularity of the layered structure. Precise temperature control of the solutions during the mixing and aging was revealed to be crucial to obtain highly regulated superlattice-like layered nanostructure after the HT treatment. The optical absorption edge of the superlattice samples showed a large blue-shift of compared to that of bulk TiO2, which can be accounted for electron confinement effects within the titanium oxide layers. Au ions were intercalated by using a phase-transfer catalyst into the hydrophobic interior of bilayer micelle template interleaving the TiO2 layers, and were subsequently reduced to obtain Au nanoparticles. The samples thus prepared showed an absorption peak in the visible light region and exhibited higher photocatalytic activity compared with layered TiO2 without Au as well as commercial TiO2 (P-25). It demonstrated that the Au nanoparticles enhanced the visible light photocatalytic activity of the layered TiO2 with the superlattice structure.

開催年月日： 2014年11月

記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Jeju   国名：大韓民国  

開催年月日： 2014年8月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：福岡大学   国名：日本国  

Oxide materials are promising candidates for thermoelectric power generation from waste heat at mid-to-high temperatures. The n-type thermoelectric properties of Al-doped ZnO, ZT ~ 0.3 at 1273 K, were first reported by the authors in 19961). Recently, we have obtained the ZT values of ~0.55 and ~0.65 at around 1273 K for nanostructured Al-doped ZnO and dually doped ZnO with Al and Ga, respectively2,3). These results strengthen the opportunity of using polycrystalline ZnO for low-cost practical waste heat harvesting. However, controversial results reported by several research groups on the thermoelectric performance of Al-doped ZnO have caused argument on the candidacy of ZnO-based thermoelectric materials. Therefore, it is noteworthy to investigate the influences of temperature and atmosphere on the thermoelectric properties of Al-doped ZnO systematically. In the present paper, thermoelectric properties of ZnO doped with Al and/or other transition metals are investigated by thermally cycling the samples under various atmospheres, particularly focusing on the possible changes in the electrical conductivity and Seebeck coefficient. Repeated cycling from room temperature to 1273 K is carried out to examine the high-temperature stability of the oxide in the oxidative and inert atmospheres. The thermogravimetric analysis is also carried out up to 1573 K in order to investigate the non-stoichiometry of the oxide and to determine the desorbing species in various atmospheres at high temperature. The results of the thermal cycling up to 1273 K in air clearly showed that the electrical conductivity and Seebeck coefficient of Al-doped ZnO sintered in N2 certainly changed during the first heating (H1), causing a large hysteresis in the first cycle (H1+C1). However, strikingly, the properties measured on the second heating (H2) were identical to those observed on the first cooling (C1), and hence the data corrected on the second cycle (H2+C2) reproduced those on C1, showing no hysteresis in the second cycle. These results demonstrate that the first heating in air up to 1273 K stabilizes the electrical properties of Al-doped ZnO sintered in N2. The details and the upper limit of the stable temperature range will be discussed.

開催年月日： 2014年7月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Nashville, TN   国名：アメリカ合衆国  

Oxide thermoelectric materials, which are highly durable at high temperature in air, non-toxic, low cost with minimal environmental impact, are apparently promising for recuperation of decentralized waste heat energy at the temperature range of > 400 °C, where all the non-oxide candidate materials will eventually be oxidized under aerobic conditions. Although strongly ionic characters of oxide materials has been regarded as an inherent disadvantage leading to low carrier mobility and high lattice thermal conductivity, it has been revealed that such disadvantages are not always the case with all oxides. Recent reports on reduced ferroelectric oxides [1] and cage-like structure oxides [2] are convincing that the simple picture of ionic compounds no longer holds for these oxides. In this paper, some new aspects in metal oxides that show unconventionally enhanced phonon scattering will be highlighted in terms of their transport properties and crystal structures. In particular, β-pyrochlore oxides ABB’O6 (A = K, Rb, Cs) show lower lattice thermal conductivity with decreasing the mass and size of the A-site alkali cations, clearly evidencing that the larger size mismatch between the A-site cations and the surrounding oversized cage framework enhances the “rattling” motion of the A-site cations and thereby efficiently shortens the phonon mean free path more for the smaller A-site cations. As a consequence, the thermal conductivity of the oxide with the smallest A cation, KBB’O6, was revealed to be virtually the same with its theoretical minimum, κmin [3].

開催年月日： 2014年6月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Montecatini Terme   国名：イタリア共和国  

Increasing energy demands in worldwide definitely require safer energy security options. Thermoelectric (TE) conversion is becoming more and more of vital importance for higher overall energy efficiency. In terms of durability at high temperature in air, metal oxides are most attractive. Since the early 1990s, several oxide materials such as CaMnO3, ZnO, SrTiO3, NaCoO2, and Ca3Co4O9 have been reported to show a promising thermoelectric performance. However, strongly ionic characters and the light constituent element, oxygen, of metal oxides are apparently against the conventional guiding principles for higher ZT. In this paper, we report the thermal and electrical properties of defect pyrochlore (β-pyrochlore) oxides AB2O6 with the “rattler-in-a-cage” structure, in which small A cations sit in an oversized cage-like crystal structure. Extremely shortened phonon mean free path with smaller A cations of in the oxides will be reported. Moreover, improvement in the electrical conduction in the B2O6 framework of the oxides will be discussed.

開催年月日： 2014年3月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：東京工業大学   国名：日本国  

開催年月日： 2014年3月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：九州大学筑紫地区   国名：日本国  

開催年月日： 2013年11月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：ESA/ESTEC, Noordwijk   国名：オランダ王国  

開催年月日： 2013年10月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Université de Rennes 1, Rennes   国名：フランス共和国  

開催年月日： 2013年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：名古屋大学   国名：日本国  

開催年月日： 2013年8月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Resorts World Sentosa   国名：シンガポール共和国  

開催年月日： 2013年8月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Portland   国名：アメリカ合衆国  

開催年月日： 2013年7月

記述言語：日本語  

開催地：北九州国際会議場   国名：日本国  

開催年月日： 2013年6月 - 2013年7月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：神戸国際会議場   国名：日本国  

開催年月日： 2013年6月 - 2013年7月

記述言語：日本語  

開催地：神戸国際会議場   国名：日本国  

開催年月日： 2013年6月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：San Diego   国名：アメリカ合衆国  

開催年月日： 2013年1月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：仙台国際センター   国名：日本国  

開催年月日： 2012年11月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Daegu   国名：大韓民国  

開催年月日： 2012年10月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Miskolc-Lillafured   国名：ハンガリー共和国  

開催年月日： 2012年9月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Yokohama   国名：日本国  

開催年月日： 2012年9月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：名古屋大学   国名：日本国  

開催年月日： 2012年8月

記述言語：英語  

開催地：Ho Chi Minh   国名：ベトナム社会主義共和国  

開催年月日： 2012年7月

記述言語：英語  

開催地：Aalborg   国名：デンマーク王国  

開催年月日： 2012年5月

記述言語：英語  

開催地：Strasbourg   国名：フランス共和国  

開催年月日： 2012年4月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Corfu   国名：ギリシャ共和国  

Increasing energy demands in worldwide definitely require safer energy security options. Moreover, the threat of the nuclear power plant disaster after the massive tsunami attack in Japan in March 2011 has obviously been making energy policies in Japan and many other countries shift more toward renewable energies. Thermoelectric power generation is one of the most promising energy options for better energy efficiency by recovering a huge amount of unused waste heat energy, which is currently unable to utilize and thus discarded. Thermoelectric (TE) power generation directly converts heat (more strictly a temperature difference) to electricity by exploiting the thermoelectric effects in solid semiconductor materials. However, conventional TE materials such as Bi2Te3 and PbTe are unlikely to accomplish wide commercialization in our society because of their toxicity, poor heat resistance, and low abundance of the comprising elements. In terms of durability and stability at high temperature in air, oxide materials are obviously most attractive. Among them, ZnO [1,2] is one of the prospective n-type oxide thermoelectric materials showing a fairly high figure-of-merit, Z = S2σ/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity. In fact, the power factor, S2σ, is large enough for Al-doped ZnO to be competitive to conventional non-oxide materials such as PbTe and Si-Ge alloys. Nevertheless, the light constituting elements and strong interatomic bonding in ZnO results in a very high κ compared to conventional thermoelectric materials based on heavy elements, limiting the Z values relatively low [1,2]. In this paper, simultaneous doping of ZnO with two or more elements is investigated in order to reduce the lattice thermal conductivity, κph, a contribution of lattice vibration or phonons to the total thermal conductivity κ = κph + κel. Analyses of the carrier mobility and κph revealed that a selective reduction of κph with maintaining relatively high σ values (selective phonon scattering) would be operative in ZnO doped with Al and Ga [3]. Moreover, binary doping of Al and Cu resulted in further intense and anomalous reduction of κ. The phonon scattering will be discussed in terms of the phonon mean free path and nanostructure in the oxide with concerning the theoretical prediction of the lower limit of κ in ZnO. References [1] M. Ohtaki, T. Tsubota, K. Eguchi, H. Arai, J. Appl. Phys., 79, 1816-1818 (1996). [2] T. Tsubota, M. Ohtaki, K. Eguchi, H. Arai, J. Mater. Chem., 7, 85-90 (1997). [3] M, Ohtaki, K, Araki, K. Yamamoto, J. Electron. Mater., 38, 1234-1238 (2009).

開催年月日： 2012年3月

会議種別：口頭発表（一般）  

開催地：Berlin   国名：ドイツ連邦共和国  

開催年月日： 2012年3月

会議種別：口頭発表（一般）  

開催地：京都市   国名：日本国  

開催年月日： 2012年3月

会議種別：口頭発表（一般）  

開催地：京都市   国名：日本国  

開催年月日： 2012年1月

会議種別：口頭発表（一般）  

開催地：Daytona Beach   国名：アメリカ合衆国  

開催年月日： 2011年12月

開催地：Hawaii   国名：アメリカ合衆国  

開催年月日： 2011年9月

会議種別：口頭発表（一般）  

開催地：Thessaloniki   国名：ギリシャ共和国  

開催年月日： 2011年9月

会議種別：口頭発表（一般）  

開催地：Warsaw   国名：ポーランド共和国  

開催年月日： 2011年9月

会議種別：口頭発表（一般）  

開催地：札幌市   国名：日本国  

開催年月日： 2011年8月

会議種別：口頭発表（一般）  

開催地：札幌市   国名：日本国  

開催年月日： 2011年8月

会議種別：口頭発表（一般）  

開催地：鹿児島市   国名：日本国  

開催年月日： 2011年7月

会議種別：口頭発表（一般）  

開催地：Traverse City   国名：アメリカ合衆国  

開催年月日： 2011年7月

会議種別：口頭発表（一般）  

開催地：Traverse City   国名：アメリカ合衆国  

開催年月日： 2011年7月

会議種別：口頭発表（招待・特別）  

開催地：Cairns   国名：オーストラリア連邦  

開催年月日： 2011年6月

会議種別：口頭発表（一般）  

開催地：Stockholm   国名：スウェーデン王国  

開催年月日： 2011年4月

開催地：San Francisco   国名：アメリカ合衆国  

開催年月日： 2011年4月

会議種別：口頭発表（一般）  

開催地：Las Vegas   国名：アメリカ合衆国  

開催年月日： 2011年3月

会議種別：口頭発表（招待・特別）  

開催地：横浜市   国名：日本国  

開催年月日： 2011年3月

会議種別：口頭発表（一般）  

開催地：浜松市   国名：日本国  

開催年月日： 2010年12月

会議種別：口頭発表（一般）  

開催地：Waikiki   国名：アメリカ合衆国  

開催年月日： 2010年11月 - 2010年12月

会議種別：口頭発表（一般）  

開催地：Boston   国名：アメリカ合衆国  

開催年月日： 2010年11月

会議種別：口頭発表（一般）  

開催地：Osaka   国名：日本国  

開催年月日： 2010年11月

会議種別：口頭発表（一般）  

開催地：Osaka   国名：日本国  

開催年月日： 2010年11月

会議種別：口頭発表（一般）  

開催地：Osaka   国名：日本国  

開催年月日： 2010年9月

会議種別：口頭発表（一般）  

開催地：Biarriz   国名：フランス共和国