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Yang A.,Japan National Institute of Materials Science | Sakata O.,Japan National Institute of Materials Science | Sakata O.,Synchrotron X ray Group | Sakata O.,Tokyo Institute of Technology | And 8 more authors.
Journal of Applied Crystallography | Year: 2015

Cubic type room-temperature (RT) epitaxial Li0.5Ni0.5O and NiO thin films with [111] orientation grown on ultra-smooth sapphire (0001) substrates were examined using synchrotron-based thin-film X-ray diffraction. The 1 1 and 2 2 rocking curves including six respective equivalent reflections of the Li0.5Ni0.5O and NiO thin films were recorded. The RT B 1 factor, which appears in the Debye-Waller factor, of a cubic Li0.5Ni0.5O thin film was estimated to be 1.8 (4) Å2 from its 1 1 and 2 2 reflections, even though the Debye model was originally derived on the basis of one cubic element. The corresponding Debye temperature is 281 (39) K. Furthermore, the B 2 factor in the pseudo-Debye-Waller factor is proposed. This parameter, which is evaluated using one reflection, was also determined for the Li0.5Ni0.5O thin film by treating Li0.5Ni0.5O and NiO as ideal NaCl crystal structures. A structural parameter for the atomic disorder is introduced and evaluated. This parameter includes the combined effects of thermal vibration, interstitial atoms and defects caused by Li doping using the two Debye-Waller factors. © 2015 International Union of Crystallography.


Aimi A.,Gakushuin University | Inaguma Y.,Gakushuin University | Kubota M.,Gakushuin University | Mori D.,Gakushuin University | And 4 more authors.
Solid State Ionics | Year: 2015

The solid state oxide Li-ion conductors with high electrochemical stability as well as high ionic conductivity are needed for application to all-solid-state Li-ion battery. In this study, A 3Li x Ta6- x Zr x Si4O26 (A =Sr and Ba) as the candidate solid electrolytes stable against Li metal were synthesized by a conventional solid state reaction, and their structure and ionic conductivities were investigated. Both the compounds with A =Sr and Ba crystallize in hexagonal structure with space group P 6-2m in the same as A 3Ta6Si4O26 does. MEM analysis, first principles calculation, and NMR spectroscopy showed that Li ions reside in interstitial sites. The sample with A =Ba exhibits higher ionic conductivity (e.g. 6.9×10-8 Scm-1 at 500K in x =1.0) than that with A =Sr (e.g. 3.2×10-8 Scm-1 at 500K in x =1.0). Ionic conductivity was enhanced with an increase of the substitution of Li and Zr. Further enhancement of ionic conductivity was derived by making deficiencies at A site cation. Consequently, Ba2.75Li1.5Ta5ZrSi4O26 exhibits the highest total ionic conductivity of 4×10-7 S/cm at 500K and the lowest activation energy of 0.72eV. The consideration of the size of bottlenecks and nudged elastic band calculations suggest that Li ions diffuse in the A-site deficient layer perpendicular to the c-axis. © 2015 Elsevier B.V.


Aimi A.,Gakushuin University | Inaguma Y.,Gakushuin University | Kubota M.,Gakushuin University | Mori D.,Gakushuin University | And 4 more authors.
Solid State Ionics | Year: 2016

The solid state oxide Li-ion conductors with high electrochemical stability as well as high ionic conductivity are needed for application to all-solid-state Li-ion battery. In this study, A3LixTa6 - xZrxSi4O26 (A = Sr and Ba) as the candidate solid electrolytes stable against Li metal were synthesized by a conventional solid state reaction, and their structure and ionic conductivities were investigated. Both the compounds with A = Sr and Ba crystallize in hexagonal structure with space group P6¯2m in the same as A3Ta6Si4O26 does. MEM analysis, first principles calculation, and NMR spectroscopy showed that Li ions reside in interstitial sites. The sample with A = Ba exhibits higher ionic conductivity (e.g. 6.9 × 10- 8 S cm- 1 at 500 K in x = 1.0) than that with A = Sr (e.g. 3.2 × 10- 8 S cm- 1 at 500 K in x = 1.0). Ionic conductivity was enhanced with an increase of the substitution of Li and Zr. Further enhancement of ionic conductivity was derived by making deficiencies at A site cation. Consequently, Ba2.75Li1.5Ta5ZrSi4O26 exhibits the highest total ionic conductivity of 4 × 10- 7 S/cm at 500 K and the lowest activation energy of 0.72 eV. The consideration of the size of bottlenecks and nudged elastic band calculations suggest that Li ions diffuse in the A-site deficient layer perpendicular to the c-axis. © 2015 Elsevier B.V. All rights reserved.

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