La10W2O21: An Anion-Deficient Fluorite-Related Superstructure with Oxide Ion Conduction

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• 作者：Marie-Hélène Chambrier ; Armel Le Bail ; Fabien Giovannelli ; Abdelkrim Redja?mia ; Pierre Florian ; Dominique Massiot ; Emmanuelle Suard ; Fran?ois Goutenoire
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：January 6, 2014
• 年：2014
• 卷：53
• 期：1
• 页码：147-159
• 全文大小：769K
• ISSN：1520-510X

文摘

The crystal structure of La₁₀W₂O₂₁, which has to be reformulated (La_5.667W_0.333)LaWO₁₄鈻?sub>2, is best described, on average, by a 2 脳 2 脳 2 anion-deficient fluorite-related superstructure cubic cell, with space group F4̅ 3m, Z = 4, and a = 11.17932(6) 脜, similar to Y₇ReO_14鈥?未. The 32 cations are distributed with lanthanum on the 4a-site, tungsten on the 4b-site, and a partial occupancy of the 24g-site by La (94%) and W. The 56 oxygen atoms occupy four 16e-sites, three of them fully and with an occupancy of 1/2 for the fourth one. Others M₁₀W₂O₂₁ (M = Er, Y) adopt a 3 脳 2 脳 2 fluorite superstructure with W in octahedral sites, whereas W is mainly in tetrahedral sites in La₁₀W₂O₂₁. Several powerful techniques such as crystal image furnace synthesis, ¹³⁹La nuclear magnetic resonance (NMR) and convergent beam electron diffraction (CBED) were used to achieve our results. Transmission electron microscopy (microdiffraction, CBED, and Tanaka patterns) brought us the real symmetry, showing that indeed classical cubic twinning along the 3-fold axis does take place. The surprising La/W mixed site is nicely confirmed by ¹³⁹La NMR. This compound exhibits interesting fast oxide ion conducting properties, comparable with LAMOX (Lacorre et al. Nature 2000, 404, 856鈥?58) at low temperature. As opposed to many ionic conductors, no temperature structural transition is observed. Its conductivity is about 6.4 脳 10^鈥? S路cm^鈥? at 700 掳C.