Papers by Akihide Kuwabara
The Journal of Physical Chemistry B, 2004
First-principles calculations with projector augmented wave method has been carried out for Sr-an... more First-principles calculations with projector augmented wave method has been carried out for Sr-and/or Mgdoped rhombohedral LaGaO 3 . The formation energies of 10 kinds of defects have been systematically computed in consideration of temperature and oxygen partial pressure. Sr 2+ ion is found to be stable at La site rather than Ga site, whereas Mg 2+ ion is stable at Ga site. The solution of dopants accompanied with the formation of oxygen vacancies shows the lowest energy at temperatures of 500-1600 K and oxygen partial pressure of 10 -21 to 1 atm. Defects resulting in n-or p-type conductivity are energetically unfavorable under these conditions. The present theoretical results are consistent with experimental results of doped LaGaO 3 in the literature regarding both site preference of dopants and the dependence of ionic conductivity on oxygen partial pressure. Substituting Sr 2+ and Mg 2+ ions with the formation of O 2vacancies are confirmed to be predominant defects in temperatures of 500-1600 K and oxygen partial pressures of 10 -21 to 1 atm in r-LaGaO 3 by means of first principles calculation.
MATERIALS TRANSACTIONS, 2004
Temperature and strain rate dependence on high temperature elongation to failure in fine-grained ... more Temperature and strain rate dependence on high temperature elongation to failure in fine-grained ceramics is phenomenologically explained from grain growth behavior during deformation and the superplastic flow behavior. The elongation to failure at temperatures between 1573 and 1773 K was analyzed for 2 mol% TiO 2 and 2 mol% GeO 2 co-doped tetragonal zirconia polycrystal (TZP), which exhibits excellent high temperature ductility. The improvement in the high temperature ductility in TZP is attributed to dopant cation segregation in the vicinity of the grain boundaries. The phenomenological analysis revealed that co-doping of Ti and Ge cations increases the grain size at the time of failure, as a parameter to describe a limit of an accommodation process for superplastic flow. The parameter of the critical grain size at the time of failure correlates well with the value of overlap population in cation-doped TZP model cluster obtained from a first-principle molecular orbital calculation. The covalent bond at the grain boundaries plays a critical role in the high temperature tensile ductility of TZP.
固体酸化物燃料電池の量子材料設計
Materia Japan, 2005
無機結晶イオン伝導体の量子材料設計
Electrochemistry, 2007
セラミック材料 第一原理分子軌道計算法による安定化ジルコニアの相安定性評価
Journal of the Society of Materials Science, Japan, 2001
Thin Films: Structural Distortion and Compositional Gradients Adjacent to Epitaxial LiMn 2 O 4 Thin Film Interfaces (Adv. Mater. Interfaces 8/2014)
Advanced Materials Interfaces, 2014
Analysis of proton creation mechanism of trivalent cations doped BaZrO3 by first principles calculations
First Principles Calculations of Oxygen Adsorption on a Stepped Pt (211) Surface
Chemical Expansion and Change in Lattice Constant of Y-Doped BaZrO 3 by Hydration/Dehydration Reaction and Final Heat-Treating Temperature
Journal of the American Ceramic Society, 2013
ABSTRACT Knowledge of thermal behavior of electrolyte is important for fuel cell fabrication. In ... more ABSTRACT Knowledge of thermal behavior of electrolyte is important for fuel cell fabrication. In this study, using high-temperature X-ray diffraction analysis (HT-XRD) and thermo-mechanical analysis (TMA), a systematic investigation of lattice constants was performed on Y-doped BaZrO3, which is a promising candidate for electrolyte in protonic ceramic fuel cells. The results revealed that a chemical expansion was observed between 300°C and 450°C during the heating process in HT-XRD, and was attributed to the dehydration of BZY. Furthermore, it was found that the lattice constants of the samples doped with Y, Sm, Eu, and Dy were larger for the ones finally heat-treated at 1600°C for sintering than those heat-treated at 1300°C for synthesizing. The similar behavior was not observed in Sc-doped samples.
First-principles study of vacancy formation in hydroxyapatite
Physical Review B, 2007
First-principles plane-wave calculations were performed for hydroxyapatite (HAp) in order to inve... more First-principles plane-wave calculations were performed for hydroxyapatite (HAp) in order to investigate the electronic structure and vacancy formation mechanisms. The HAp unit cell contains PO4 tetrahedra and OH groups formed by covalent P-O and H-O bonds. Ca ions play a role for connecting the PO4 tetrahedra and OH groups in an ionic character of bonding. It is found that OH-
Science and Technology of Advanced Materials, 2007
First-principles calculations based on density functional theory enable us to quantify the therma... more First-principles calculations based on density functional theory enable us to quantify the thermal equilibrium concentration of a point defect through calculating the formation energy of the defect. In order to know the formation energy, we need three parameters: the energy difference between defective and perfect systems, chemical potential of constitutive atoms and Fermi level. The energy difference is obtained from calculations based on ''supercell method''. The energy of a supercell with a charged defect should be corrected by an appropriate way such as alignment of electrostatic potential. The chemical potential and Fermi level can be fixed from conditions of phase equilibrium and charge neutrality. r
Advanced Energy Materials, 2013
Concerted efforts continue to be made in the search for superior lithium-ion conducting solids to... more Concerted efforts continue to be made in the search for superior lithium-ion conducting solids to replace the highly reactive liquid electrolytes typically used in rechargeable batteries. LISICON-type materials have been studied extensively over the last few decades, providing abundant experimental data, but to date no overall design principle for achieving high conductivity has been forthcoming. In this communication we present results of systematic sets of fi rst-principles calculations based on the cluster expansion method, as well as fi rst-principles molecular dynamics (FPMD) simulations carried out to calculate Li-ion conductivities at high temperature, for a diverse range of compositions. A machine-learning technique is used to combine theoretical and experimental datasets to predict the conductivity of each composition at 373 K. The insights obtained show that an iterative combination of fi rst-principles calculations and focused experiments can greatly accelerate the materials design process by enabling a wide compositional and structural phase space to be examined effi ciently.
Epitaxial Growth of LiMn 2 O 4 Thin Films by Chemical Solution Deposition for Multilayer Lithium-Ion Batteries
The Journal of Physical Chemistry C, 2014
Cubic and orthorhombic structures off aluminum hydride AlH3 predicted by a first-principles study
First Principles Calculations of Advanced Nitrides, Oxides and Alloys
Key Engineering Materials, 2009
ChemInform Abstract: First-Principles Investigation of R 2 O 3 (ZnO) 3 (R: Al, Ga, and In) in Homologous Series of Compounds
ChemInform, 2008
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Superplastic Behavior in Small Amount of Ge-Ti Co-Doped TZP
Materials Science Forum, 2004
Impact of local strain on Ti-L₂,₃ electron energy-loss near-edge structures of BaTiO₃: a first-principles multiplet study
Microscopy (Oxford, England), 2014
Identification of local strains is crucial because the local strains largely influence the ferroe... more Identification of local strains is crucial because the local strains largely influence the ferroelectric property of BaTiO₃. The effects of local strains induced by external pressures on the Ti-L₂,₃ electron energy-loss near-edge structure (ELNES) of BaTiO₃ were theoretically investigated using first-principles multiplet calculations. We revealed that the effects appear in the position of the spectral threshold, namely the spectrum shifts to lower and higher energy sides by the tensile and compressive pressures, respectively. We concluded that conventional ELNES observations can identify only large strains induced by -10 GPa, and 0.1 eV energy resolution is required to identify ±2% of strains.
A-site vacancies and atomic-scale domain boundary structures in polycrystalline solid-state electrolyte Li0. 34La0. 51TiO3
Special Issue on Grain Boundaries, Interfaces, Defects and Localized Quantum Structures in Ceramics-Interface/Grain Boundary Phenomena-Criterion for High Temperature Failure and Grain Boundary
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Papers by Akihide Kuwabara