Crystal Structure and Oxide-Ion Conductivity of Highly Grain-Aligned Polycrystalline Lanthanum Germanate Oxyapatite Grown by Reactive Diffusion between Solid La2GeO5 and Gases [G

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• 作者：Koichiro Fukuda ; Toru Asaka ; Shinji Hara ; Abid Berghout ; Emilie B茅chade ; Olivier Masson ; Jenny Jouin ; Philippe Thomas
• 刊名：Crystal Growth & Design
• 出版年：2015
• 出版时间：July 1, 2015
• 年：2015
• 卷：15
• 期：7
• 页码：3435-3441
• 全文大小：401K
• ISSN：1528-7505

文摘

We prepared the highly c*-axis-aligned polycrystalline lanthanum germanate oxyapatite, La_9.68Ge₆O_26.52, by the reactive diffusion that occurs between a randomly grain-oriented La₂GeO₅ polycrystal and [GeO + 1/2O₂] gases at 1723 K in air. The resulting La_9.68Ge₆O_26.52 polycrystal was examined by optical microscopy, X-ray diffractometry, micro-Raman spectroscopy, and impedance spectroscopy. The crystal structure (space group P1) showed the appreciable positional disordering of 9 of the 24 O atoms, bonding to Ge atoms, in the unit cell. We have found an extra O site, with the occupation factor of 0.51, which was located close to one of the six Ge sites with the Ge鈥揙 distance of 鈭?.198 nm. The Raman extra band at 649 cm^鈥? also suggested the existence of the five coordinate Ge atoms. The conductivity along the c* axis of oxide ions steadily increased from 6.3 脳 10^鈥? to 1.04 脳 10^鈥? S/cm as the temperature increased from 573 to 973 K. The activation energy of conduction was 1.2 eV.