Language：English  

The behavior of hydrogen (H) as an impurity in indium (In)-doped tin dioxide (SnO₂) was investigated by mass spectrometry analyses, with the aim of understanding the charge compensation mechanism in SnO₂. The H-concentration of the In-doped SnO₂ films increased to (1-2)×10¹⁹cm^-3 by annealing in a humid atmosphere (WET annealing). The electron concentration in the films also increased after WET annealing but was two orders of magnitude less than their H-concentrations. A self-compensation mechanism, based on the assumption that H sits at substitutional sites, is proposed to explain the mismatch between the electron- and H-concentrations.

DOI： 10.1063/1.4870425

Language：English  

DOI： 10.1002/adma.200903953

Language：English   Publisher：The Ceramic Society of Japan  

<p>Thickly and densely sintered electrodes (TDSE) consisting of active materials can achieve highly capacitive Li-ion batteries and are one of the ideal electrode structures applicable for co-sintered-type solid-state batteries based on oxide-based solid electrolytes. This study focused on Li₃<i>_x</i>La_2/3−<i>_x</i>TiO₃ (LLTO) as the TDSE for the anode. LLTO exhibits high Li-ion conductivity and a high capacity of 225 mAh g⁻¹ with an operation potential below 1 V (vs. Li⁺/Li). However, the electronic conductivity of LLTO is low (less than 10⁻⁸ S cm⁻¹), and the improved electronic conductivity seems necessary. In this paper, we investigated the electrochemical properties of LLTO sintered electrodes and improved the electronic conductivity of LLTO by Mn substitution for the Ti site. LLTO shows a huge overpotential during initial Li insertion due to low electronic conductivity of 1.1 × 10⁻⁹ S cm⁻¹, resulting in extremely low capacity. On the other hand, Mn substitution enhances the electronic conductivity, resulting in improved first-cycle charging properties.</p>

DOI： 10.2109/jcersj2.24116

Scopus

CiNii Research

Language：Japanese   Publisher：The Electrochemical Society of Japan  

<p></p>

DOI： 10.5796/denkikagaku.22-fe0027

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ceramint.2022.04.224

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2109/jcersj2.21183

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.snb.2021.131256

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10853-021-06214-4

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.snb.2020.128999

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.200748

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acsaelm.0c00902

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acsomega.0c04846

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acssensors.0c01365

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5796/electrochemistry.20-00121

Language：English   Publishing type：Research paper (scientific journal)  

Language：English  

Nowadays, monitoring and recording CO₂ gas has become more and more important in various areas, leading to increasing demand for developing high-sensitive CO₂ sensors. In this study, a novel potentiometric CO₂ gas sensor is designed based on a new solid electrolyte of Y-doped La_9.66Si_5.3B_0.7O_26.14 (Y-LSBO), coated with the Li₂CeO₃-Au-Li₂CO₃ composite as a sensing electrode and Pt as a reference electrode. With the optimized composition of a sensing electrode, the electromotive force (EMF) varies linearly with the logarithm of the CO₂ concentration in the range of 400-4000 ppm, exhibiting an excellent Nernstian response to CO₂ gas in both dry and humid atmospheres. The fabricated CO₂ sensor can be well operated at 400 °C in a dry atmosphere and 450 °C in a humid atmosphere. Based on the results, we have proposed that the good CO₂ sensing performance may be associated with Li₂CeO₃ playing a role of "ionic bridge" between the O^2- conductor (Y-LSBO) and the Li⁺ conductor (Li₂CO₃). This study not only shows the promising potential of a Y-LSBO solid electrolyte utilized in the field of gas sensors but also enriches the research of solid electrolyte-based potentiometric CO₂ gas sensors.

DOI： 10.1021/acsami.0c00454

Language：Japanese  

Language：English   Publishing type：Research paper (other academic)  

Miniaturized semiconductor gas sensors composed of microheater and a sensor electrode allowed a rapid heater switching, pulse-driven operation. SnO₂ nanoparticles was fabricated on the gas sensor device, and the sensor was driven during heater on phase at elevated temperature. Additionally, the gas was introducing into the sensing layer during heater off phase, cooling the sensing layer. On the basis of the behavior of the electrical resistance under pulse-driving, we determined the various types of sensor responses to improve the gas sensing characteristics. The gas sensitivity was drastically enhanced by pulse-driving mode, because utility factor of the pulse-driven sensor was higher than that of conventional sensor. Additionally, newly gas sensing definition also enhanced the gas selectivity, because gas accumulates in the sensing layer during heater off phase. Therefore, pulse-driving mode improved the ability of semiconductor gas sensors.

DOI： 10.1109/ISOEN.2019.8823211

Language：English  

Oxygen adsorption on the surface of particles plays a key role in gas sensing for SnO₂-based resistive-type gas sensors in a humid atmosphere. In this study, we added an extremely small amount of ZrO₂ on the SnO₂ surface to activate oxygen adsorption and enhance the sensor response of a SnO₂-based gas sensor in a humid atmosphere. We evaluated the oxygen adsorption properties and sensor response to 200 ppm H₂ in a humid atmosphere (96&#37;) based on variations in the measured electrical resistance. The adsorption of O⁻ and O²⁻ ions was activated by a small loading (0.033 mol&#37;) of ZrO₂, and the resulting ZrO₂–SnO₂ composite nanoparticles were in the deep electron-depleted state. This led to a high sensor response of ZrO₂–SnO₂ to H₂ in a humid atmosphere. The results demonstrate that surface modification using an extremely small amount of ZrO₂ was effective in improving the response of a SnO₂-based gas sensor in a humid atmosphere.

DOI： 10.1007/s10853-018-3020-y

Language：English  

A new electrochemical oxygen separation pump was developed by using c-axis-oriented La _9.66 Si _5.3 B _0.7 O _26.14 (c-LSBO), which has high oxide-ionic conductivity (>10 ¹³ S cm ¹¹ ) up to 300°C. Interfacial resistance between the electrode and c-LSBO was investigated to realize the full potential of LSBO as an oxygen separation material. The formation of a Sm-doped CeO ₂ (SDC) thin film (thickness: 300 nm) between the electrode and c-LSBO was effective for suppressing the interfacial resistance. Furthermore, a mixed conductive La _0.6 Sr _0.4 Co _0.78 Ni _0.02 Fe _0.2 O ₃ ¹ _¤ (LSCFN) was applied to the electrode for enhancing the oxygen reduction/evolution activity on the electrode. The LSCFN/SDC/c-LSBO symmetric cell showed an oxygen permeation flux of 3.5 mL cm ¹² min ¹¹ (1.0 A cm ¹² ) at 600°C under an applied DC voltage of 1.5 V; this value was 67 times that of Pt/c-LSBO. This oxygen pump based on the LSCFN/SDC/c-LSBO symmetric cell would find promising application in oxygen separation at intermediate temperatures. Further reduction of the interfacial resistance and polarization resistance of the electrode may decrease the operating temperatures to below 400°C.

DOI： 10.2109/jcersj2.18172

Language：English  

In this study, the influence of the oxygen partial pressures (PO2) on the sensor response to H₂ of SnO₂ resistive-type gas sensors was evaluated under various humid atmospheres. SnO₂ nanoparticles of 8–15 nm in diameter were synthesized using a hydrothermal technique followed by calcination at 600°C. Additionally, a large amount of pores with diameters greater than 10 nm was confirmed in the nanoparticles. The electrical resistance at 350°C was decreased with decreasing the P_O2, and the electrical resistance in the presence of 10 ppm H₂ was much smaller than that in the absence of H₂ in both dry and humid atmospheres regardless of the P_O2. Furthermore, the sensor response to 10 ppm H₂ at 350°C increased with decreasing P_O2 in both dry and humid atmospheres. Thus, decreasing the amount of oxygen adsorption enhanced the effect of rooted hydroxyl formation on the SnO₂ surface through a combustion reaction between H₂ and adsorbed oxygen and improved the sensor response to H₂. These results are important for understanding the fundamental mechanisms of gas detection and for the material surface design of highly sensitive resistive-type semiconductor gas sensors.

DOI： 10.1149/2.1391906jes

Language：English  

Improvements in the responses of semiconductor gas sensors and reductions in their detection limits toward volatile organic compounds (VOCs) are required in order to facilitate the simple detection of diseases, such as cancer, through human-breath analysis. In this study, we introduce a heater-switching, pulse-driven, micro gas sensor composed of a microheater and a sensor electrode fabricated with Pd-SnO₂-clustered nanoparticles as the sensing material. The sensor was repeatedly heated and allowed to cool by the application of voltage to the microheater; the VOC gases penetrate into the interior of the sensing layer during its unheated state. Consequently, the utility factor of the pulse-driven sensor was greater than that of a conventional, continuously heated sensor. As a result, the response of the sensor to toluene was enhanced; indeed, the sensor responded to toluene at levels of 1 ppb. In addition, according to the relationship between its response and concentration of toluene, the pulse-driven sensor in this report can detect toluene at concentrations of 200 ppt and even lower. Therefore, the combination of a pulse-driven microheater and a suitable material designed to detect toluene resulted in improved sensor response, and facilitated ppt-level toluene detection. This sensor may play a key role in the development of medical diagnoses based on human breath.

DOI： 10.1021/acs.analchem.8b03076

Language：English  

A thick bulk-sized Li₇La₃Zr₂O₁₂ (LLZ) solid electrolyte is successfully prepared using a polymer complex method and a hot isostatic pressing (HIP) treatment. Despite the difficulties of densification, HIP-treated LLZ can be prepared as a transparent ceramic pellet because of its ~200 μm primary grain size, and its conductivity is improved by its increased density (>99&#37;). An all-solid-state lithium battery is fabricated by using a mixed conducting ionic liquid gel to connect the bulk-sized LLZ electrolyte and a LiFePO₄ (LFP) cathode. The introduction of the mixed conducting gel layer reduces the electrode/electrolyte interface resistance. The specific discharge capacity of the active cathode material is 169 mAh g⁻¹ (current density of 0.046 mA cm⁻²), which suggests that almost the full capacity of LFP can be utilized even under the all-solid-state cell design. The coulombic efficiency (ηc) is ≈1, and no side reactions are observed. The LFP/LLZ/Li cell shows a high electrochemical stability against the Li metal anode, and the cell operates for 20 cycles without dendrite growth causing a short circuit under a charge current density of 0.591 mA cm⁻² (1/2 C rate).

DOI： 10.1016/j.ssi.2018.02.029

Language：English  

For monitoring of air quality and medical diagnosis, metal-oxide-semiconductor particles with high sensitivity to detect small amount of gases are desirable. Herein, we report the fabrication of ZnO pyramid-shaped particles with remarkably high sensitivity to ethanol gas. The ZnO pyramid-shaped particles were synthesized solvothermally under agitation from the solution of zinc acetate anhydride, hexamethylenetetramine, ethylene glycol, and water. Gas sensing response was evaluated as the ratio of electrical resistance of the ZnO particulate layer in air to that in ethanol. The agitation during the solvothermal process resulted in dispersion of the pyramid-shaped particles rather than spherical aggregates. TEM studies revealed that the base of the pyramid-shaped particles is the (0001) plane and that the six side surfaces are the {101 1} plane. The highest gas sensing response value to 50 ppm ethanol gas was about 10※000, which is remarkably higher than that of previously reported ZnO particles. The influence of the crystal facets and the polarity is discussed.

DOI： 10.1021/acs.jpcc.8b01936

Language：English  

To understand the relationship between adsorbed oxygen on the surface of indium oxide (In
₂
O
₃
) and its CO-sensing property in wet and dry atmospheres, the oxygen adsorption properties and sensor response to CO were investigated. In
₂
O
₃
particles were prepared by a precipitation method and characterized using X-ray diffraction, scanning electron microscopy, and nitrogen absorption measurements. The O− and O
²⁻
adsorption equilibrium constants, K
₁
and K
₂
, respectively, were calculated from the relationship between the electrical resistance and the oxygen partial pressure (P
_O2
) using a competitive adsorption model. It was found that the values of both K
₁
and K
₂
decreased with increasing humidity, indicating a reduction in the amount of oxygen adsorption on the In
₂
O
₃
surface in a wet atmosphere. The In
₂
O
₃
particles can detect CO at ppm level in dry and wet atmospheres, although they were greatly reduced in wet atmospheres. Moreover, we found that the sensor response to CO is closely related to the values of K
₁
and K
₂
.

DOI： 10.1149/2.0591807jes

Language：English  

To investigate the effect of aging at 580 °C in wet air (humid aging) on the oxygen adsorption on the surface of SnO₂ particles, the electric properties and the sensor response to hydrogen in dry and humid atmospheres for SnO₂ resistive-type gas sensors were evaluated. The electric resistance in dry and wet atmospheres at 350 °C was strongly increased by humid aging. From the results of oxygen partial pressure dependence of the electric resistance, the oxygen adsorption equilibrium constants (K₁; for O^- adsorption, K₂; for O^2- adsorption) were estimated on the basis of the theoretical model of oxygen adsorption. The K₁ and K₂ in dry and wet atmospheres at 350 °C were increased by humid aging at 580 °C, indicating an increase in the adsorption amount of both O^- and O^2-. These results suggest that hydroxyl poisoning on the oxygen adsorption is suppressed by humid aging. The sensor response to hydrogen in dry and wet atmosphere at 350 °C was clearly improved by humid aging. Such an improvement of the sensor response seems to be caused by increasing the oxygen adsorption amount. Thus, the humid aging offers an effective way to improve the sensor response of SnO₂ resistive-type gas sensors in dry and wet atmospheres.

DOI： 10.3390/s18010254

Language：English  

W-doped ZnO films are synthesized by pulsed laser deposition on Al2O3(1120) substrate, and their gas-sensing properties are investigated. Significantly improved sensitivity and response time to ethanol vapor are achieved. In order to study the relation between high sensing performance and local structure around the dopant W site, we carry out two-dimensional photoelectron diffraction on W-doped ZnO thin films at two different annealing temperatures (600 and 1000 °C). The photoelectron-intensity angular-distribution (PIAD) patterns of Zn 3p and W 4f core levels show the presence of forward-focusing peaks of very different relative intensities in the bulk and surface. From the PIAD patterns and their circular dichroism, we find clear evidence for the substitution of a segregated W atom into a Zn site in the second atomic layer. The result shows a direct relationship between the drastic increase in gas-sensing performance via W doping and the segregation of W at the surface. It also demonstrates that this photoelectron-diffraction measurement is a powerful tool for the study of the local structure of dopant sites in gas-sensing materials.

DOI： 10.1103/PhysRevApplied.7.064029

Language：English  

SiO₂/SnO₂ core-shell nanofibers were synthesized using TEMPO-oxidized cellulose nanofibers as templates. The gas sensing properties of the synthesized SiO₂/SnO₂ core-shell nanofibers were evaluated under dry and humid conditions and compared to practical SnO₂ nanoparticles produced by a hydrothermal method. The sensor responses were analyzed by monitoring the electric resistance changes upon the introduction of H₂ or CO analytes. Surprisingly, the SiO₂/SnO₂ nanofibers showed a prominent sensor response at a higher temperature at which the adsorbed oxygen on the SnO₂ nanoparticles desorbs under dry conditions. Unexpectedly, the SiO₂/SnO₂ nanofibers are available in humid atmosphere since they are less influenced by H₂O poisoning compared to the SnO₂ nanoparticles. Such an intriguing phenomenon could be interpreted in terms of the lower susceptibility of the major adsorbed oxygen species toward water vapor.

DOI： 10.1039/c7tc01642e

Language：English   Publishing type：Research paper (scientific journal)  

Many studies in the past decade have sought to explore the origin and evolution of water in planetary bodies based on the hydrogen isotopic compositions of apatite. However, no investigation has studied hydrogen diffusivity in apatite. This work reports hydrogen diffusion experiments using a natural Durango fluorapatite carried out under a saturated 2H₂O/O2 vapor flow at temperatures of 500-700 °C. Diffusion depth profiles for 1H and 2H were measured using secondary ion mass spectrometry (SIMS), indicating that 2H diffusion occurred by an exchange reaction between the original ¹H and ²H during annealing. Hydrogen diffusion coefficients were obtained by the fitting of diffusion profiles of ²H using Fick's second law; they followed an Arrhenius-type relationship. The temperature dependence of hydrogen diffusion parallel to the c-axis at 500-700°C can be expressed as D=6.71×10^-13exp(-80.5 ±3.3/RT)[m/s] Hydrogen diffusion coefficients in apatite are several orders of magnitude greater than those of other elements. Hydrogen diffusion in apatite occurs at relatively low temperatures (below 700°C). This study indicates that the hydrogen isotopic compositions of apatite are readily affected by the presence of water vapor through the ¹H-²H exchange reaction without changing the total water content in the crystal.

DOI： 10.2343/geochemj.2.0460

Language：English  

LiCoO₂ is epitaxially grown on SrTiO₃ (100) substrates with (104) orientation. Because the LiCoO₂ film is grown with its c-axis parallel to four equivalent 〈111〉 axes of the SrTiO₃, the (104)-oriented film exhibits four-domain structure on the SrTiO₃ (100) substrate. Introducing off-cut angle to the substrate surface breaks the equivalency between the four 〈111〉 axes of the SrTiO₃ substrate to induce preferential growth of specific orientation with the c-axis in a descending direction of off-cut surface. Increasing off-cut angle and lowering deposition rate promote the preferential growth, because they facilitate step-flow growth mode, and finally align the c-axes in the domains completely into one 〈111〉 direction of the SrTiO₃ substrate. The LiCoO₂ film delivers a discharge capacity of 90 mAh g⁻¹ at a low discharge rate of 0.01 C, and 25&#37; of capacity is kept even at a high rate of discharge with 100 C.

DOI： 10.1016/j.jpowsour.2016.06.015

Language：English  

In this study, we prepared thermally stable SnO₂ nanocrystals (ca. 4 nm) in a mixture of SnCl₄, tetraethylene glycol (TEG), and tetrabutylammonium hydroxide (TBAH) under reflux and obtained a highly sensitive semiconductor gas sensor. It has been determined both theoretically and experimentally that the synthesis of oxide semiconductor nanoparticles is an important factor in highly sensitive semiconductor gas sensors. However, as-synthesized nanocrystals generally grow large during calcination at high temperature, and this thermal crystal growth reduces the sensor response. Therefore, to refine the response of the semiconductor gas sensor, we synthesized thermally stable SnO₂ nanocrystals by heating under reflux a SnCl₄-TBAH-TEG mixture. The obtained SnO₂ nanocrystals exhibited high thermal stability even when calcined at a temperature up to 600 °C. The gas-sensing films fabricated from the thermally stable SnO₂ nanocrystals exhibited a high sensor response to hydrogen due to their small crystal size, and a change in their surface property as compared with conventional SnO₂ nanocrystals synthesized via hydrothermal treatment.

DOI： 10.1021/acs.cgd.6b00087

Language：English  

The electrochemical performance of an all-solid-state lithium-oxygen battery was examined using a platinum patterned electrode with a lithium conducting solid electrolyte under a humidified O₂ atmosphere. The cell consisted of a lithium metal anode, a protective layer of polyethylene oxide with Li(CF₃SO₂)₂N, a lithium-conducting solid electrolyte of Li_{1 + x + y}Al_x(Ge,Ti)_{2 - x}Si_yP_{3 - y}O₁₂, and a sputtered platinum stripe-patterned air electrode. The open circuit voltage (OCV) of the virgin cell was 3.5 V under humidified O₂ and decreased to 3.2 V after slight discharge, which is comparable with that under dry O₂ (2.4 V). The cell was successfully discharged and charged at 0.1 mA cm^{- 2} and 60 °C. A reaction product was observed on the platinum electrode; however, it could not be identified by X-ray diffraction analysis or Raman spectroscopy, which indicated it was amorphous. Nano-secondary ion mass spectrometry (SIMS) analysis suggested that the reaction product contains Li, H, and O.

DOI： 10.1016/j.ssi.2016.03.003

Language：English  

Al-incorporated ZnO films with various Al concentrations were prepared using pulsed laser deposition on the (112-0) face of sapphire substrates, and their gas sensing properties were evaluated. The use of c-axis-oriented epitaxial films with the same thickness suppressed the influence of the surface-to-volume ratio and surface atomic arrangements on the sensing properties, clarifying the role of Al doping in the improvement of ZnO gas sensors. The results of ethanol gas sensing measurements indicated that Al doping significantly improved the sensing response and response time of the ZnO gas sensors. The formation of Al-related impurity phases and/or non-equilibrium defects induced by Al doping improved the sensing performance. On the other hand, changes in the grain size did not significantly affect the sensing response.

DOI： 10.2109/jcersj2.15319

Language：English  

Zinc-doped Tin-dioxide thin (SnO₂) films were synthesized on c-alumina substrates by radio-frequency (rf ) sputtering. To fabricate zinc-doped SnO₂ thin films with different concentrations of zinc, an insulating zinc-doped SnO₂ target was placed on a conductive non-doped target. Thin films were then deposited at different flow rates of argon gas. Zinc concentration in the deposited SnO₂ thin films increased with increasing flow rate of argon gas. Moreover, the SnO₂ thin film with a zinc concentration of 2.2 × 10¹⁹/cm³ showed the highest gas-sensor response. It is concluded that this rf-sputtering growth method is a useful tool for identifying suitable materials compositions for creating gas sensor with response for hydrogen and ethanol.

DOI： 10.2109/jcersj2.16015

Language：English  

This study exhibits influence of deposition rate on LiCoO₂ epitaxial films prepared by pulsed laser deposition. High deposition rates tend to destabilize trivalent Co, resulting in formation of an oxygen-deficient phase with a rock-salt structure as an impurity in the deposited films. Because the oxygen-deficient phase originates from incomplete oxidation, post-annealing in air eliminates the impurity phase. Moreover, since it also improves the crystallinity of the film, the post-annealing enhances the electrode performance of the LiCoO₂ films.

DOI： 10.1016/j.ssi.2015.06.006

Language：English   Publishing type：Research paper (other academic)  

Sensing layer mixed perovskite oxide, La_0.1Sr_0.9Co_0.4Fe_0.6O_3-δ (LSCF), and Pd-loaded SnO₂ nanoparticles (LSCF@Pd-SnO₂) was deposited on the membrane of MEMS device by injection method, and its gas sensing properties to reducing gases and VOCs were investigated by heating sensor in pulse mode with heaters in ON and OFF state for one second repeatedly. The MEMS sensor showed fast response, high sensitivity and stability to 200 ppm C₇H₈ at 250°C by pulse heating with extremely low power consumption.

DOI： 10.1149/07516.0031ecst

Language：English  

Abstract The reaction product and reaction site for solid-state lithium-air batteries were examined using a platinum pattern electrode on a lithium conducting solid electrolyte. The cell consisted of a lithium metal anode, a protective layer consisting of polyethylene oxide with the Li(CF₃SO₂)₂N lithium salt, a lithium conducting solid electrolyte of Li_{1 + x + y}Al_x(Ge,Ti)_{2 - x}Si_yP_{3 - y}O₁₂, and a sputtered platinum striped pattern air electrode. The cell was discharged at 1.0 μA cm^{- 2} for 300 h and the reaction product was analyzed using Raman spectroscopy and X-ray photoelectron spectroscopy. The reaction product of Li₂O₂ was observed at the triple phase boundaries of oxygen, platinum and electrolyte, in addition to on the platinum and solid electrolyte surfaces. This result suggests that the oxygen reduction reaction can proceed on the surface of the Li₂O₂ reaction product.

DOI： 10.1016/j.ssi.2015.06.022

Language：English  

A transparent garnet-type lithium-ion conducting solid electrolyte of 1.0 wt&#37; Al₂O₃-doped Li₇La₃Zr₂O₁₂ (A-LLZ) was prepared using hot isostatic pressing (HIP). The A-LLZ pellet sintered at 1180°C for 36 h was followed by HIP treatment at 127 MPa and 1180°C under an Ar atmosphere. The bulk conductivity of the HIP treated A-LLZ was 9.9 × 10^{- 4} S cm^{- 1} at 25°C. The Li/HIP treated A-LLZ/Li cell showed no short-circuit due to lithium dendrite formation at 0.5 mA cm^{- 2}.

DOI： 10.1016/j.ssi.2015.06.009

Language：English  

ZnO spherical powder with hierarchical structure was synthesized from zinc acetate anhydride and hexamethylenetetramine in a solvent of water and ethylene glycol (EG), and its time evolution was investigated by microscopic and isotope tracer studies. Initially, spherical ZnO particles made of nanocrystallites were precipitated. From the early growth stage, crystallites were radially aligned along the c-axis. With aging, the nanoparticles transformed into hexagonal prism-like particles with pyramidal tops, which showed clear radial alignment. Subsequently, the ZnO spheres became cracked and broke into wedge-shaped pieces of the pyramid-like particles. The microscopic studies suggested that the spherical particles grew through oriented attachment of small particles during the early growth stage, while Ostwald ripening through dissolution-recrystallization changed the component particles to a pyramidal shape in the later stage. In order to investigate the growth process, we attempted a novel isotope tracer study, where H₂¹⁸O was used for the solvent and the distribution of ¹⁸O in the spherical particles was analyzed by a secondary ion mass spectrometer. The concentric ¹⁸O distribution in the ZnO spherical powder aided the mechanism of continuous concentric-oriented attachment of nanoparticles to form spherical ZnO particles. The difference in the ¹⁸O distribution before and after transformation into the pyramid shape was small, which implies that this change was a local reaction. The oxygen isotope tracer study in water-EG solvent was proven effective in determining the history of the particles and the development of their inner structures.

DOI： 10.1021/cg5014297

Language：English  

We investigated effects of base pressure (P_base) of the deposition chamber on electrical properties and defect states of amorphous In-Ga-Zn-O (a-IGZO) thin films deposited by pulsed laser deposition. The impurity hydrogen concentration was increased by an order of magnitude when P_base was deteriorated from <10^-5 to 10^-3Pa. The optimum oxygen partial pressures (P_O2) were 2-4 Pa for an optimized deposition condition with the good P_base; on the other hand, off-optimized and/or poor P_base require much higher P_O2. This result provides an experimental evidence for a charge compensation model by excess oxygen for H-containing a-IGZO. Thermal desorption spectra indicated that the impurity hydrogens originate mainly from water molecules in the residual gas and exist as -OH chemical bonding states in the a-IGZO films. Hard X-ray photoemission spectroscopy revealed that these -OH states form deep defects above the valence band maximum.

DOI： 10.1109/JDT.2014.2358251

Language：English  

Selective oxygen separation from air was performed using perovskite-type oxide membranes made of Ba_0.95La_0.05FeO_3-δ. We demonstrated that surface modification of Ba_0.95La_0.05FeO_3-δ membranes with La_1-xSr_xFeO_3-δ catalyst layers led to an increase in oxygen permeation fluxes at 700-930 °C. We studied the effects of oxygen vacancy amounts, surface area, particles size, surface treatment of La_1-xSr_xFeO_3-δ on the oxygen permeability of the membranes fitted with La_1-xSr_xFeO_3-δ catalyst layers. Among the catalyst layers tested, the membranes fitted with La_0.9Sr_0.1FeO_3-δ (x=0.1) showed the highest oxygen permeation flux probably because of its higher porosity and uniform morphology without open voids, which would increase the number of surface reaction sites. The obtained results suggest the feasibility of further upgrading the membrane performance by using surface catalyst layers having a homogeneous morphology and a different composition from that of the mother membrane.

DOI： 10.1016/j.ceramint.2015.02.118

Language：English  

A medium-energy ion-stimulated desorption spectroscope was combined with a helium ion microscope to develop a microscope for lithium (Li) analysis with high spatial resolution below 10nm. The analysis of Li is based on time-of-flight (TOF) spectroscopy. A clear Li peak was observed in the TOF spectra for the samples containing Li. The capability of the microscope was demonstrated using a LiCoO₂/Nb doped SrTiO₃ sample. Furthermore, the Li distribution on the sample was successfully observed by measuring the Li+ peak intensity as a function of the helium irradiation position.

DOI： 10.7567/APEX.7.106601

Language：English  

The effect of crystalline polarity on the microstructure of gallium-doped zinc oxide (GZO) deposited using magnetron sputtering onto glass substrates was investigated. X-ray photoelectron spectroscopy was used to determine the crystalline polarity of c-axis textured GZO films. Grains whose radii were more than 1 μm grew abnormally in 0.2 mol&#37; doped GZO when the film was thicker than ~ 1 μm, and the radius of the grains was much smaller than 100 nm in the heavily (i.e., 4 mol&#37;) doped GZO, regardless of the film thickness. Such abnormal growth of the grains in the 0.2 mol&#37; doped GZO films coincided with a change in the crystalline polarity: the surfaces of unusually large GZO grains were terminated with the (0001̄) face, and those of normal GZO grains were terminated with the (0001) face. The results indicated that polarity flipping is a very important event for controlling the texture of doped zinc oxide films.

DOI： 10.1016/j.tsf.2013.12.017

Language：English  

We synthesized micrometer-sized ZnO spherical particles solvothermally from the solutions of zinc acetate anhydride, hexamethylenetetramine (HMT), ethylene glycol (EG) and water, and examined the gas sensing properties. The spherical powders were composed of nano particles, which were radially aligned along the c-axis. We obtained particles with smaller crystallites under conditions of higher EG concentrations and shorter reaction period. Spherical powder made of crystallites of 35 nm was precipitated in the 95 vol&#37;-EG solvent by heating at 120°C for 4 h. The ZnO powder annealed at 450°C worked as a gas sensor device for volatile organic compounds (VOC) gases. The sensitivity was the best in the case of ethanol gas at 350°C.

DOI： 10.2109/jcersj2.122.488

Language：English  

We investigated roles of hydrogen on physical properties of a-IGZO films and thin-film transistors (TFTs) by comparing standard and ultra-high vacuum (UHV) sputtering systems. It was confirmed that the impurity hydrogens come mainly from the residual gas in the deposition chamber and the molecules adsorbed to the surface of the sputtering target. It was found impurity hydrogen has unfavorable effects as follows; (i) enhances selective Zn desorption during film deposition, and (ii) weakens chemical bonds of the resulting film, causing temperature instability. On the other hand, the UHV a-IGZO films with less hydrogen had low density and exhibited structural instability, suggesting that some hydrogens would have a favorable effect to enhance structural relaxation rate and to form denser and more stable structures during film deposition at room temperature. The revealed hydrogen effects are discussed in relation to those in amorphous silicon and silicon dioxide.

DOI： 10.1149/2.015409jss

Language：English  

Hydrogen impurities in SnO₂ films and bulk ceramics were investigated in terms of mass transport and electron transport. The hydrogen concentration (n[H]) in these samples was found to be 10¹⁹ cm^-3 or higher. Further increase in n[H] could be achieved by annealing the samples in a humid atmosphere. The isotope tracer (¹H/²H exchange) study revealed that a part of the hydrogen in these samples showed rapid migration even at 300 °C. However, electrical measurements revealed that the electron concentration in the samples was much less than n[H]. These results could be explained by assuming the presence of defect-hydrogen complexes.

DOI： 10.1063/1.4863668

Language：English  

The oxygen diffusivity in BaTiO₃ thin films heteroepitaxially grown on SrTiO₃ substrates was investigated using a gas/solid exchange technique with 18O-isotope-enriched gas. Deformation of the BaTiO ₃ lattice and inhibition of the oxygen diffusivity occurred simultaneously when the YSZ layer, which is assumed to be catalytic for the 18O/16O exchange reaction, was deposited on BaTiO₃. The mechanism for the reduction in oxygen diffusivity due to the YSZ cover layer is discussed in terms of residual stress in the strained BaTiO₃ layer.

DOI： 10.2109/jcersj2.122.410

Language：English  

We synthesized ZnO nano-particulate films by a sol-gel method and evaluated their gas sensing properties. A ZnO colloidal solution of 5.6 nm sized nanocrystals was prepared from zinc acetate in n-propanol and dip-coated on silica glass substrates. The as-deposited ZnO film consisted of 30nm grains. Annealing the films resulted in a growth of the particles, which was confirmed by scanning probe microscopy and UV-Vis spectrometry. The ZnO film annealed at 400°C worked well as a gas sensor device for volatile organic compounds (VOC) gases. The sensitivity was the best in the case of ethanol gas at 350°C. The sensing performances decreased by annealing at higher temperatures due to the coalescence of the ZnO particles.

DOI： 10.2109/jcersj2.122.267

Language：English   Publishing type：Research paper (other academic)  

The effect of the surface preparation in samarium doped semiconducting barium titanate [(Ba_1-xSm_x)TiO₃] ceramics with (Ba, Sm)/Ti ratio of 1.000 was studied by means of isotope tracer technique using a secondary ion mass spectrometer. The surfaces of specimens were prepared with the chemical mechanical polishing (CMP) with colloidal silica slurry or the mechanical polishing (MP) with diamond paste. The oxygen diffusion coefficients obtained in the CMP samples were small compared to those in the mechanical polished samples. This fact suggests that the surface prepared with CMP has less oxygen defect concentration. Moreover, it was also indicated that high temperature treatment over 1000 °C is required for annihilation of defects formed by MP. The oxygen diffusion study used CMP sample brings the useful information on the oxygen defect chemistry in Sm doped BaTiO₃.

DOI： 10.4028/www.scientific.net/KEM.582.189

Language：English  

The carbon cycle of carbonate solids (e.g., limestone) involves weathering and metamorphic events, which usually occur over millions of years. Here we show that carbonate anion intercalated layered double hydroxide (LDH), a class of hydrotalcite, undergoes an ultrarapid carbon cycle with uptake of atmospheric CO₂ under ambient conditions. The use of ¹³C-labeling enabled monitoring by IR spectroscopy of the dynamic exchange between initially intercalated ¹³C-labeled carbonate anions and carbonate anions derived from atmospheric CO₂. Exchange is promoted by conditions of low humidity with a half-life of exchange of ∼24 h. Since hydrotalcite-like clay minerals exist in Nature, our finding implies that the global carbon cycle involving exchange between lithosphere and atmosphere is much more dynamic than previously thought.

DOI： 10.1021/ja4099752

Language：English  

An isotope tracer study, i.e., ¹⁸O/¹⁶O exchange using ¹⁸O₂ and H₂¹⁸O, was performed to determine how post-deposition annealing (PDA) affected surface reactivity and oxygen diffusivity of amorphous indium-gallium-zinc oxide (a-IGZO) films. The oxygen tracer diffusivity was very high in the bulk even at low temperatures, e.g., 200°C, regardless of PDA and exchange conditions. In contrast, the isotope exchange rate, dominated by surface reactivity, was much lower for ¹⁸O₂ than for H₂¹⁸O. PDA in a humid atmosphere at 400°C further suppressed the reactivity of O₂ at the a-IGZO film surface, which is attributable to -OH-terminated surface formation.

DOI： 10.1063/1.4829996

Language：English  

Scandium nitride (ScN) films were grown on (100) MgO single crystals by a molecular beam epitaxy method. The effects of growth conditions, including [Sc]/[N] ratio, growth temperature, and nitrogen radical state, on the electrical properties of the ScN films were studied. The ScN films comprised many small columnar grains. Hall coefficient measurements confirmed that the ScN films were highly degenerate n-type semiconductors and that the carrier concentration of the ScN films was sensitive to the growth temperature and the nitrogen radical states during the film growth. The carrier concentrations of the ScN films ranged from 10¹⁹-10²¹ cm^-3 while the Hall mobilities ranged from 50-130 cm²·V ^-1·s^-1 for undoped films. The temperature-dependent Hall coefficient measurements showed that the carrier concentration is nearly independent of temperature, indicating that the change in resistivity with temperature is explained by a change in the Hall mobility. The temperature-dependence of the Hall mobility was strongly affected by the growth conditions.

DOI： 10.1063/1.4820391

Language：English   Publishing type：Research paper (other academic)  

We investigated the effect of Zr impurities on the oxygen diffusion pathway in BaTiO₃ ceramics by using an ion-imaging technique. Zr impurities were introduced into BaTiO₃ ceramics by a planetary ball milling process. The oxygen tracer diffused quickly from the surface up to the grain boundary and then appeared as discontinuous steps at the grain boundary. The results indicate that the grain boundary acted as a blocking layer against oxygen diffusion. The blocking for oxygen diffusion at the grain boundary is thought to originate during the formation and distribution of complex defects between the charged oxygen vacancies and the Ba vacancies near the grain boundary.

DOI： 10.4028/www.scientific.net/KEM.566.262

Language：English  

Tin oxide (SnO₂) hollow nanofibers doped with cerium oxide (CeO_x) were synthesized to study the impact of CeO₂ additives on their chemical sensing response. X-ray diffraction analysis and Raman scattering spectroscopic analysis showed that crystallization of CeO ₂ in the fiber composites was observed only when the Ce concentration was greater than 6 mol&#37;. Also, maximum sensing response to ethanol was seen in the fiber composites with 6 mol&#37; addition of Ce. Accordingly, we have discussed the possible explanations for this, including the role of crystalline CeO ₂ as a surface catalyst, and the role of hydrogen liberated during the dehydrogenation reaction of ethanol diffusing into the SnO₂ lattice. The results obtained in this study indicate that SnO ₂-CeO₂ nanofiber composites are potential candidates for use as high-sensitivity gas sensors.

DOI： 10.1016/j.snb.2013.07.016

Language：English   Publishing type：Research paper (other academic)  

The a-axis oriented ZnO thin films deposited on (011 2) sapphire substrates by pulsed laser deposition were studied to investigate the effects of pre-annealing on oxygen diffusion. The effect was as follows: the oxygen diffusion coefficient decreased, and the oxygen concentration in the tailing regions of the profiles reduced. Ion images of an oxygen tracer revealed the high-diffusivity paths for oxygen tracer diffusion. The temperature dependence of oxygen tracer diffusion coefficients (D_b) in as-deposited and pre-annealed thin films were determined to be D_b [cm²/s] = 9.2×10² exp (-405 [kJ/mol] / RT) and D_b [cm ²/s] = 1.8×10³ exp (- 418 [kJ/mol] / RT), respectively. On basis of these results, the crystal orientation on D _b and the mechanism for oxygen diffusion were discussed.

DOI： 10.4028/www.scientific.net/KEM.566.266

Language：English  

Oxygen diffusion phenomena in BaTiO ₃ ceramics doped with Ho of 5.2×10 18/cm3 were studied in order to reveal the effect of reduction thermal annealing. The samples were reduced at 850°C in a 3&#37; H2-Ar atmosphere before the oxygen diffusion experiments. The oxygen diffusion was carried out in the temperature range of 700-800°C. The measurement of diffusion profiles and ion images revealed the oxygen defect distribution caused by the annealing. The results show that the grain boundary acts as a layer blocking oxygen diffusion when the diffusion temperature is below the reduction temperature of 850°C.

DOI： 10.1143/JJAP.51.101801

Language：English  

Isotopic ZnO thin films were deposited on the c-plane of ZnO single crystals by pulsed laser deposition. The isotopic abundance of Zn in the films was determined with a secondary ion mass spectrometry before and after the films was diffusion annealed. The diffusion profiles across the film/substrate interface behaved smooth features. The zinc diffusion coefficient (D _Zn) was obtained by analyzing the slope of the profile in the annealed sample. The temperature dependence of D _Zn was determined to be D _Zn(cm ²/s)=8.0×10 ⁴exp(-417[kJ/mol])/ RT, where R and T are gas constant and temperature. The zinc ion diffusion coefficients were of the same order as that in a ZnO single crystal. A comparison of the experimental and theoretical values indicated that the zinc ions diffused in the thin film and the single crystal through a vacancy mechanism.

DOI： 10.1016/j.ssc.2012.07.002

Language：English  

We report an unique planar defect that draws the Nazca Lines in epitaxially grown La _2/3-xLi _3xTiO ₃ (LLTO) (x ≈ 0.11) ion-conductive perovskite. Transmission electron microscopy and electron energy loss spectroscopy reveal that the lines are produced by changing the regular arrangement of alternate stacks of La-rich and La-poor layers along the c-axis into all La-rich layers near the defect. The first-principle calculation suggests that the La-rich layers should act as a barrier to Li conductivity and are, therefore, important for the application of epitaxially grown LLTO thin films.

DOI： 10.1063/1.4744886

Language：English  

Aluminum-doped zinc oxide ceramics were used to study oxygen self-diffusion by the vapor-solid exchange method. The diffusion profile and the quantitative analysis of impurities (H, Li, and Al) were performed by secondary ion mass spectrometry. The concentrations of Al and H in ZnO were evaluated to be 3.2 × 10¹⁹ and below 1.5 × 10¹⁷/cm³, respectively. The simultaneous diffusion of oxygen tracer and Li impurity were detected in the analysis, and the diffusion profiles were analyzed to evaluate the diffusion coefficients. Enhanced oxygen diffusivity and increased Li impurity concentration was obtained in Al-doped ZnO. We discuss the defect equations for enhancing oxygen diffusivity and increasing Li concentration in Al-doped ZnO.

DOI： 10.1143/JJAP.50.125501

Language：English  

Effect of Al-substitution for Co on the electrode properties of LiCoO ₂ is investigated in a sulfide solid electrolyte. The substitution decreases the electrode resistance and thus improves the high-rate capability. Investigation of the post-annealing effect revealed that, although the crystal structure or morphology of the LiAl_xCo_1-xO₂ are not significantly changed by the post-annealing, the electrode properties are highly dependent on the post-annealing conditions, which suggests that the improvement in high-rate capability comes from the change in surface structure of the LiAl_xCo_1-xO₂ particles (i.e., self-organized core-shell structure). The Al-substituted LiCoO₂ obtained through this study delivers a discharge capacity of 115 mAh g ^-1 at 1 C and 84 mAh g^-1 even at a high discharge rate of 5 C at 25 °C, which is one of the highest rate capabilities observed in solid-state cells.

DOI： 10.1021/cm103665w

Language：English  

We performed visualization of the oxygen diffusion path in oxidized and reduced BaTiO₃ ceramics by utilizing an ion-imaging technique. The oxygen tracer diffused quickly from the surface up to the grain boundary, and then behaved as discontinuous steps at the grain boundary. The grain boundary acted as a blocking layer against oxygen diffusion. The reduction process enhanced the blocking effect. The blocking of oxygen diffusion at the grain boundary originated in the formation and distribution of complex defects between the charged oxygen vacancy and the reduced Ti near the grain boundary.

DOI： 10.1143/APEX.4.055801

Language：English   Publishing type：Research paper (other academic)  

To determine the effect of the annealing atmosphere on oxygen diffusion through Ba_0.95La_0.05FeO_3-δ pellets, ¹⁸O₂ tracer diffusion and high-resolution secondary ion mapping were performed. When annealing in air, the ¹⁸O concentration around the surface up to a depth of 40 μm was almost constant. On the other hand, when annealing in vacuum, the ¹⁸O concentration obviously decreased. High-resolution secondary ion mapping indicated that the ¹⁸O concentration around the grain boundary was reduced. These results suggested that the grain boundary of BLF annealed in vacuum prevents oxygen diffusion.

DOI： 10.4028/www.scientific.net/KEM.485.141

Language：English  

SnO₂ thin films were grown on silica glass substrates using the pulsed laser deposition (PLD) method, and their structures, electric properties, and sensor performances were examined to investigate the sensing mechanism of thin-film gas sensors. Single-phase SnO₂ films with rutile-type structures were obtained at 650 °C. All the SnO₂ films had many columnar grains, and the grain size increased with film thickness. Measurements of the Hall coefficient at room temperature revealed that the Hall mobility of the films was independent of the film thickness. In contrast, the sensing performances of the films for NO₂ and H₂ gases respectively in an air atmosphere drastically improved for film thicknesses under 100 nm. These results for the film properties and sensing performances of SnO₂ thin films are discussed in terms of a space-charge layer formed on the columnar grains.

DOI： 10.1016/j.snb.2010.07.036

Language：English  

We carried out the partial substitution of the B-site in BaFeO _3-δ perovskite with divalent cations to develop novel oxygen-permeable materials. We demonstrated that the partial substitution of Cu or Ni by more than 10&#37; resulted in the stabilization of the cubic perovskite structure even at room temperature in a highly oxygen-permeable phase, as revealed by the X-ray diffraction (XRD) analysis. The Cu substitution was more effective for the stabilization, because the introduction of Cu in the lattice more effectively made the Goldschmidt tolerance factor (t) close to 1.0. Ni- and Cu-substituted BaFeO_3-δ membranes showed higher oxygen permeabilities than their parent BaFeO_3-δ membranes particularly at lower temperatures around 600700 °C owing to the stabilization of the cubic phase. Among the fabricated membranes, a BaFe _0.85Cu_0.15O_3-δ membrane (1.0 mm thickness) showed the highest oxygen permeation flux (1.8 cm³ min^-1 cm^-2 at 930 °C) under an air/He gradient. The results indicated that Cu-substituted BaFeO_3δ is promising as a material for Co-free membranes with high oxygen permeabilities.

DOI： 10.1016/j.jssc.2010.08.002

Language：English  

Selective oxygen separation from air was carried out using ceramic membranes composed of Ba_0.95La_0.05FeO_3-δ. We demonstrated that surface abrasion of Ba_0.95La _0.05FeO_3-δ membranes led to a significant increase in oxygen permeation fluxes at 700-930 °C because of an increase in surface reaction sites. Abrasion of the oxygen desorption side of the membrane resulted in a higher oxygen permeability than with abrasion on the oxygen sorption side. Moreover, an increase in the area of the oxygen desorption side also increased the oxygen permeability. The results suggest that oxygen permeation through Ba_0.95La_0.05FeO_3-δ membranes is limited by the desorption of oxygen (surface reaction) and bulk diffusion. Attachment of a porous layer made of Ba_0.95La_0.05FeO _3-δ to the membrane surface was also effective in increasing oxygen permeability. For example, a high permeation flux of 3.2 cm³ min^-1 cm^-2 was achieved at 930 °C under a He/air gradient for a membrane (0.5 mm thickness) coated with a porous layer (14.4 μm).

DOI： 10.1021/am100524k

Language：English  

Mixed ionic-electronic conductors are materials which conduct both oxide ions and electronic charge carriers (electron and/or hole) simultaneously. Perovskite-type oxides (ABO₃) with valence-variable cations and oxide ion vacancies such as La_1-xSr_xCo_1-yFe _yO_3-δ (LSCFs) are representative and most intensively studied mixed conductors. LSCFs and their relatives desorb and absorb a large amount of oxygen reversibly from and into the crystal lattice without changing their fundamental crystal structures. By full use of the reversible oxygen sorption-desorption and mixed conductive properties, oxygen separation from, for example, air with 100&#37; selectivity is possible at temperatures above 300 °C. High temperature oxygen separation is very important technology to recover waste heat from high-temperature facilities and can contribute the improvement of energy efficiencies. Oxygen separation is also a key technology for oxy-fuel combustion, because its exhaust consists, in principle, of H₂O and CO₂ which is ready for CCS (Carbon dioxide Capture and Storage). In this review article, two types of oxygen separation technologies by using mixed ionic-electronic conductors are outlined; membrane separation at high temperature range (usually above 800 °C) and temperature/pressure swing separation at medium to high temperature range (for example, 300-800 7deg;C). After describing basic aspects of mixed conductive perovskite-type oxides, current research status and future challenges will be reviewed.

Language：English  

In order to investigate the effect of the microstructure on the oxygen permeation in Ba_0.95La_0.05FeO_3-δ membranes, three different methods such as solid-state reaction, nitrate and acetate decomposition (NAD), and amorphous malic acid precursor (AMP) methods were used to fabricate membranes with different grain sizes. The grain size of the membranes was successfully controlled from 35 to 829 μm² via sintering at 1175°-1275°C. The oxygen permeation fluxes through the Ba_0.95La_0.05FeO_3-δ membranes increased with a decrease in the grain size. The AMP method, using malic acid as a complexing agent, produced a membrane having the highest oxygen permeability (3.10 cm³·(min·cm²)^-1 at 930°C) and the smallest grain size. The results obtained again confirmed the significant importance of microstructure control in designing high-performance oxygen permeable membranes.

DOI： 10.1111/j.1551-2916.2010.03700.x

Language：English  

ZnO samples added with MgO of 1.411.7mol&#37; were used for studying oxygen diffusion by the vaporsolid exchange method. The analyses of oxygen diffusion profiles and impurities were performed by secondary-ion mass spectrometry (SIMS). The results indicate that the increase of MgO concentration enhances oxygen diffusion. The difference between the bulk-diffusion coefficients of oxygen for ZnO samples added with MgO of 1.4 and 11.7mol&#37; was about two orders of magnitude. It was found that the grain boundary diffusion coefficients of oxygen in ZnO with 11.7mol&#37; of MgO were larger than those in other samples, by a factor of about 10. Above results indicate that MgO addition into ZnO increases the concentration of effective defects for that promote oxygen diffusion. As the effective defects, the possibilities of vacancy and interstitial of oxygen are discussed.

DOI： 10.2109/jcersj2.118.362

Language：English  

Silver implantation (75 keV, 2 × 10¹⁴ ions/cm²) in ZnO ceramics was carried out at room temperature to characterize the diffusion phenomenon. Annealing caused Ag evaporation from the sample. Results suggest that it is difficult to incorporate Ag into Zn site by annealing. The Ag profile with the monotonous decrease in concentration below 3 × 10 ¹⁷/cm³ was observed in ZnO annealed at 900°C. Above results become the basic results for producing the ZnO sensor used the reaction at surface and the grain boundary.

DOI： 10.2109/jcersj2.118.217

Language：English  

In order to perform a high throughput exploration of sensor materials using surface plasmon resonance (SPR), the gas sensing property of a ZnO/Au/SiO ₂ chip with SPR and the enhancing effect of UV irradiation on the desorption rate of NO₂ from the ZnO surface were investigated. When the ZnO/Au/SiO₂ chip was exposed to a high concentration of NO ₂ (1000 ppm), a large peak shift was observed in the SPR curve. However, this sensing signal for NO₂ gas did not recover to the baseline. In the case of low-concentration NO₂ (10 ppm), the peak shift of the SPR curve was lower than that in the case of the high-concentration gas, but recovery to the baseline was observed. From the X-ray photoelectron spectra for N 1s of the ZnO thin films exposed to 1000- and 10-ppm NO ₂, two chemisorption states-NO₂ ^- (403.7 eV) and NO₃ ^- (407 eV)-were confirmed. After the ZnO film was irradiated by UV rays, exposed to 10-ppm NO₂, all peaks related to N 1s disappeared. However, in the case of the ZnO film exposed to 1000-ppm NO ₂, adsorbed NO₃ ^- remained on the surface of ZnO. From these results, it was found that UV irradiation effectively assisted NO₂ desorption from the surface of the ZnO thin film exposed to 10-ppm NO₂.

DOI： 10.2109/jcersj2.118.193

Language：English   Publishing type：Research paper (other academic)  

The relationship between Al and Li during diffusion was studied using Al-implanted ZnO. The Al donor in ZnO acts to increase the concentration of Li contamination from the atmosphere during the annealing. It is difficult to decompose the relationship formed by diffusion between Al and Li during high-temperature annealing. The most effective method to decompose the relationship is to anneal the as-implanted ZnO at a pressure of 5×10 ^-3 torr. This annealing increases the Al solubility limit because the ZnO surface evaporates.

DOI： 10.4028/www.scientific.net/KEM.445.205

Language：English  

Partially Zr-substituted BaFe _1-yZr _yO _3-δ membranes were developed as a Co-free oxygen permeable membrane. In order to stabilize the cubic perovskite structure, Fe sites in BaFeO _3-δ were partially substituted with Zr ⁴⁺. In the substitution range of y=0.01-0.1, the cubic perovskite structure was stabilized even at room temperature. Among the membranes prepared, a BaFe _0.975Zr _0.025O3 _-δ material (y=0.025) showed the highest oxygen permeation flux of 1.30 cm3 (standard temperature pressure) min-1 cm-2 at 930°C under an air/He gradient. The oxygen permeation flux was higher than that of partially Ce-substituted BaFe _1-yCe _yO _3-δ membranes reported previously. From the results obtained by chemical and scanning electron microscope analyses, it appears that the oxygen permeability for BaFe _1-yZr _yO _3-δ membranes was well correlated with the amount of oxygen defects in the lattice as well as the grain size. In addition, the oxygen permeation flux of the BaFe _0.975Zr _0.025O3 _-δ membrane was significantly increased after decreasing the thickness of the membrane from 2.0 to 0.4 mm. For thin membranes (0.4-1.0 mm), the thickness dependence of the oxygen permeability deviated from the Wagner equation, suggesting that the oxygen permeation of BaFe _0.975Zr _0.025O3 _-δ is controlled by not only bulk diffusion of oxide ions but also their surface reactions.

DOI： 10.1149/1.3086763

Language：English   Publishing type：Research paper (scientific journal)  

To achieve a high oxygen permeation rate at medium and high temperature, an asymmetrically structured membrane, in which a thin dense layer (30μm) made of La _0.6Ca _0.4CoO _3-δ (LCC) and BaFe _0.975Zr _0.025O _3-δ (BFZ) was formed on a porous LCC support, was fabricated and tested for its oxygen permeability. The oxygen permeation flux significantly increased by mixing BFZ with LCC and reached a fairly high value of 1.60 cm ³ min ^-1 cm ^-2 even at 780°C.

DOI： 10.1246/cl.2009.94

Language：English   Publishing type：Research paper (scientific journal)  

To explore oxygen permeable materials, oxygen permeation properties of partially A-site substituted BaFe O_3-δ perovskites were investigated. Ba sites in BaFe O_3-δ were substituted with cations such as Na, Rb, Ca, Y, and La by 5%. The partial substitution with Ca, Y, and La, whose ionic radii are smaller than that of Ba, succeeded in stabilizing a cubic perovskite structure that is a highly oxygen permeable phase, as revealed by X-ray diffraction analysis. This can be explained in terms of a decrease in the tolerance factor (t). Among the Ba_0.95 M _0.05 Fe O_3-δ (M = Na, Rb, Ca, Y, and La) membranes tested, Ba_0.95 La_0.05 Fe O_3-δ showed the highest oxygen permeability at 600-930°C, owing to the stabilization of the cubic phase without the formation of impurity phases. From chemical analysis, the oxygen permeability of Ba_1-x La_x Fe O _3-δ membranes was correlated with the amount of oxygen defects (δ) in the lattice. The oxygen permeation flux of Ba_0.95 La_0.05 Fe O_3-δ membrane was significantly increased by reducing its thickness. Furthermore, a Ba_0.975 La_0.025 Fe O_3-δ membrane exhibited good phase stability under He flow at elevated temperatures. The obtained results indicate the promising properties of Ba_1-x La_x Fe O3-δ membranes as a cobalt-free material that has a high oxygen permeability, good phase stability, and low cost.

DOI： 10.1149/1.3231690

Language：English  

To achieve high-efficiency oxygen permeation using mixed (ionic and electronic) conducting perovskite-type oxides, we examined asymmetric-structured membranes of La_0.6Ca_0.4CoO₃ in which a thin dense membrane was deposited on a porous support. The La_0.6Ca _0.4CoO₃ porous support was fabricated using irregular-shaped precursor particles prepared through an oxalate method. The fabricated support had good gas permeability and thermal stability, showing sufficient properties as a support for dense thin membranes. A dense membrane of 10 μm thickness was successfully formed on the porous support by coating a La_0.6Ca_0.4CoO₃ slurry and subsequent densification by sintering. The deposited thin membrane was gastight and free from clacks, as revealed by gas permeation tests and SEM observations. The asymmetric membrane exhibited a high oxygen permeability of 1.66 cm³ (STP, standard temperature and pressure) min^-1 cm^-2 at 930 °C, which was four times higher than that of a typical sintered-disk type membrane with 1200 μm thickness, demonstrating its feasibility as a high-performance oxygen separation membrane.

DOI： 10.1021/cm8013144

Language：English  

An asymmetric-structured membrane, in which a dense thin La_0.6Ca_0.4CoO₃ layer of 10 μm was deposited on porous La_0.6Ca_0.4CoO₃ support by a slurry dropping method, were tested for its oxygen permeability at 630-930 °C. In order to increase the oxygen permeability, porous La_0.6Ca_0.4CoO₃ and SrCo_0.8Fe_0.2O_{3 - δ} oxygen evolution layers were attached on the dense layer. It was found that the asymmetric structured membranes with the porous oxygen evolution layers showed remarkably higher oxygen permeability as compared with a conventional sintered disk-type membrane (1200 μm). This suggests that oxygen permeation through membranes of 10 μm in thickness is rate-determined by both bulk O^2- diffusion and oxygen evolution reaction. The maximum oxygen permeability reached 4.77 cm³ (STP) min^{- 1} cm^{- 2} (3.54 × 10^{- 6} mol cm^{- 2} s^{- 1}) at 930 °C for the asymmetric membrane with porous La_0.6Ca_0.4CoO₃ oxygen evolution layer of 10 μm in thickness (STP = Standard Temperature and Pressure). Further improvements in the oxygen permeability would be achieved through control of the micro-structure of the oxygen evolution layers.

DOI： 10.1016/j.ssi.2007.12.092

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Soul   Country：Korea, Republic of  

Event date： 2017.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Tainan   Country：Taiwan, Province of China  

Event date： 2020.10

Language：English  

Country：Japan  

Event date： 2020.5

Language：English  

Country：Japan  

Event date： 2020.5

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.3

Language：Japanese  

Country：Japan  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：コテージ・ヒムカ(宮崎市山崎町浜山)   Country：Japan  

Event date： 2019.7

Language：English   Presentation type：Oral presentation (general)  

Venue：LEXINGTON CONVENTION CENTER   Country：Japan  

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.7

Language：English   Presentation type：Oral presentation (general)  

Venue：つくば国際会議場   Country：Japan  

Event date： 2019.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Tsukuba International Congress Center   Country：Japan  

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：PyeongChang Alpensia Resort Convention Center(Pyeong chang-Gun Gangwon-Do), Korea   Country：Japan  

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：PyeongChang Alpensia Resort Convention Center(Pyeong chang-Gun Gangwon-Do), Korea   Country：Japan  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都大学 吉田キャンパス   Country：Japan  

Event date： 2019.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台国際センター   Country：Japan  

他元素置換により立方晶構造を安定化したガーネット型Li7La3Zr2O12(LLZ)は、室温で1.0×10-4 S cm-1以上の高いLiイオン導電性を示し、Li金属に対して高い安定性を示すことから、全固体Liイオン二次電池用固体電解質として注目を集めている。複数の単セルを積層したバイポーラ構造を有する全固体電池の作製には、電極部材と固体電解質の一体焼結が必要とされているが、LLZの焼結には1000ºC以上の高温を要するため、電極材料の分解や電極材料とLLZの反応により高抵抗界面が形成する問題がある。そのため、LLZの焼結温度を大幅に低減する必要がある。我々はこれまでに、低融点Liイオン導電性酸化物であるLi3BO3のリチウムサイトにAl3+を置換したLi2.46Al0.18BO3（LABO）とAl置換LLZを複合化させることで、低温・短時間での焼結特性が改善することを見出している[1]。しかしながら、そのイオン導電率は、1.0×10-6 S cm-1と報告されている値を大きく下回っていた。これは、複合固体電解質中のLABの分布が不均一なため焼結が不十分であり、十分なイオン伝導パスが形成されていないことに起因すると考えられた。そこで、本研究では、メカニカルミリング法により均一なLLZ/LAB複合固体電解質を作製し、その低温焼結挙動について検討した。

Event date： 2019.1 - 2019.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台国際センター   Country：Japan  

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本市国際交流会館(熊本市中央区花畑町4-18)   Country：Japan  

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本市国際交流会館(熊本市中央区花畑町4-18)   Country：Japan  

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Best Western Arirang-Hill hotel, 8 Arirang-ro, Seoul, Korea   Country：Japan  

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Best Western Arirang-Hill hotel, 8 Arirang-ro, Seoul, Korea   Country：Japan  

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Best Western Arirang-Hill hotel, 8 Arirang-ro, Seoul, Korea   Country：Japan  

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Best Western Arirang-Hill hotel, 8 Arirang-ro, Seoul, Korea   Country：Japan  

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Best Western Arirang-Hill hotel, 8 Arirang-ro, Seoul, Korea   Country：Japan  

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Best Western Arirang-Hill hotel, 8 Arirang-ro, Seoul, Korea   Country：Japan  

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Best Western Arirang-Hill hotel, 8 Arirang-ro, Seoul, Korea   Country：Japan  

Event date： 2018.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Best Western Arirang-Hill hotel, 8 Arirang-ro, Seoul, Korea   Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋工業大学(名古屋市昭和区御器所町)   Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋工業大学(名古屋市昭和区御器所町)   Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋工業大学(名古屋市昭和区御器所町)   Country：Japan  

Event date： 2018.9

Language：English   Presentation type：Oral presentation (general)  

Venue：名古屋工業大学(名古屋市昭和区御器所町)   Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ホテルグリーンピア南阿蘇   Country：Japan  

Event date： 2018.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場(北九州市小倉北区浅野3-9-30)   Country：Japan  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Perugia   Country：Italy  

Event date： 2018.6

Language：English  

Venue：Perugia   Country：Italy  

Event date： 2018.3

Language：Japanese  

Venue：東北大学川内北キャンパス   Country：Japan  

Event date： 2018.3

Language：Japanese  

Venue：東京理科大学葛飾キャンパス   Country：Japan  

Event date： 2018.3

Language：Japanese  

Venue：東京理科大学葛飾キャンパス   Country：Japan  

SnO2半導体MEMSガスセンサにおいて、加熱、冷却を短時間で繰り返す間歇駆動することで、冷却時に被検ガスがセンサ膜内部まで拡散することで、加熱初期にセンサ感度が大幅に増加することを報告した。また、加熱時のセンサ応答の経時変化がガス種に大きく依存することから、波形解析により、ガス選択性を付与できることも見出した。

Event date： 2018.1

Language：Japanese  

Venue：つくば国際会議場（エポカル/EPOCHAL）   Country：Japan  

Event date： 2018.1

Language：Japanese  

Venue：つくば国際会議場（エポカル/EPOCHAL）   Country：Japan  

Event date： 2017.11

Language：English  

Country：Japan  

Event date： 2017.11

Language：English  

Country：Japan  

Event date： 2017.11

Language：English  

Country：Japan  

Event date： 2017.11

Language：English  

Country：Japan  

Event date： 2017.11

Language：English  

Country：Japan  

Event date： 2017.11

Language：English  

Country：Japan  

Event date： 2017.11

Language：English  

Country：Japan  

Event date： 2017.11

Language：English  

Country：Japan  

Event date： 2017.11

Language：English  

Country：Japan  

Event date： 2017.11

Language：English  

Country：Japan  

Event date： 2017.11

Language：English  

Venue：Pan Pacific Hanoi, Vietnam（Hanoi）   Country：Viet Nam  

Event date： 2017.11

Language：English  

Venue：Pan Pacific Hanoi   Country：Viet Nam  

Event date： 2017.11

Language：English  

Venue：Pan Pacific Hanoi, Vietnam（Hanoi）   Country：Viet Nam  

Event date： 2017.10

Language：Japanese  

Venue：ユニオンビル(武蔵小杉）   Country：Japan  

Event date： 2017.9

Language：Japanese  

Venue：神戸大学   Country：Japan  

Event date： 2017.9

Language：Japanese  

Venue：神戸大学   Country：Japan  

Event date： 2017.9

Language：Japanese  

Venue：神戸大学   Country：Japan  

Event date： 2017.9

Language：Japanese  

Venue：神戸大学   Country：Japan  

Event date： 2017.9

Language：Japanese  

Venue：長崎大学   Country：Japan  

Event date： 2017.9

Language：Japanese  

Venue：長崎大学   Country：Japan  

Event date： 2017.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2017.7

Language：Japanese  

Venue：北九州国際会議場   Country：Japan  

Event date： 2017.5

Language：English  

Venue：名古屋大学   Country：Japan  

Event date： 2017.5

Language：English  

Venue：名古屋大学   Country：Japan  

Event date： 2017.3

Language：Japanese  

Venue：日本大学   Country：Japan  

Event date： 2017.3

Language：Japanese  

Venue：日本大学   Country：Japan  

Event date： 2017.1

Language：Japanese  

Venue：岡山コンベンションセンター   Country：Japan  

Event date： 2016.11

Language：English  

Venue：ハインズ・コンベンション・センター   Country：United States  

Event date： 2016.10

Language：English  

Venue：Hawaii Convention Center & Hilton Hawaiian Village   Country：United States  

Event date： 2016.10

Language：English  

Venue：Hawaii Convention Center & Hilton Hawaiian Village   Country：United States  

Event date： 2016.9

Language：Japanese  

Venue：広島大学（東広島キャンパス・東広島市鏡山一丁目4 番5号）   Country：Japan  

Event date： 2016.9

Language：Japanese  

Venue：広島大学（東広島キャンパス・東広島市鏡山一丁目4 番5号）   Country：Japan  

Event date： 2016.9

Language：Japanese  

Venue：広島大学（東広島キャンパス・東広島市鏡山一丁目4 番5号）   Country：Japan  

Event date： 2016.9

Language：Japanese  

Venue：広島大学（東広島キャンパス・東広島市鏡山一丁目4 番5号）   Country：Japan  

Event date： 2016.7

Language：Japanese  

Venue：?九州国際会議場   Country：Japan  

Event date： 2016.7

Language：Japanese  

Venue：?九州国際会議場（?九州市小倉?区浅野3?9?30）   Country：Japan  

Event date： 2016.7

Language：Japanese  

Venue：?九州国際会議場（?九州市小倉?区浅野3?9?30）   Country：Japan  

Event date： 2016.7

Language：Japanese  

Venue：?九州国際会議場   Country：Japan  

Event date： 2016.6 - 2016.11

Language：Japanese  

Venue：京都大学   Country：Japan  

Event date： 2010.9 - 2010.10

Language：English  

Venue：Korea University   Country：Korea, Republic of  

Event date： 2010.1

Language：Japanese  

Venue：沖縄コンベンションセンター   Country：Japan  

Event date： 2010.1

Language：Japanese  

Venue：沖縄コンベンションセンター   Country：Japan  

Event date： 2009.9

Language：Japanese  

Venue：東京農工大学   Country：Japan  

Event date： 2009.5

Language：English  

Venue：大分   Country：Japan  

Event date： 2009.3

Language：Japanese  

Venue：京都大学   Country：Japan  

Event date： 2009.3

Language：English  

Venue：Indonesia   Country：Indonesia  

Event date： 2008.11

Language：English  

Venue：Chikushi Campus, Kyushu University   Country：Japan  

Event date： 2008.10

Language：English  

Venue：KOREA   Country：Korea, Republic of  

Event date： 2008.10

Language：English  

Venue：America,Hawaii   Country：United States  

Event date： 2008.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：山梨大学   Country：Japan  

Language：English  

Country：Other  

Language：Japanese  

Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Other  

Language：English  

Country：Other  

Language：English  

Country：Other  

Language：English  

Country：Other  

Language：English  

Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Other  

Language：English  

Country：Other  

Language：Japanese  

Country：Other  

Language：English  

Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：10

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：14

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：6

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：2