Synthesis, properties and phase transitions of pyrochlore- and fluorite-like Ln<sub>2sub>RMO<sub>7sub> (Ln = Sm, Ho; R = Lu, Sc; M = Nb, Ta)

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• 作者：A.V. Shlyakhtina ; D.A. Belov ; K.S. Pigalskiy ; A.N. Shchegolikhin ; I.V. Kolbanev ; O.K. Karyagina
• 关键词：Oxides ; Ionic conductivity ; Phase transitions ; Thermal expansion ; Magnetic properties
• 刊名：Materials Research Bulletin
• 出版年：January, 2014
• 年：2014
• 卷：49
• 期：Complete
• 页码：625-632
• 全文大小：1630 K

文摘

We have studied the new compounds with fluorite-like (Ho<sub>2sub>RNbO<sub>7sub> (R = Lu, Sc)) and pyrochlore-like (Sm<sub>2sub>ScTaO<sub>7sub>) structure as potential oxide ion conductors. The phase formation process (from 1200 to 1600 掳C) and physical properties (electrical, thermo mechanical, and magnetic) for these compounds were investigated. Among the niobate materials the highest bulk conductivity is offered by the fluorite-like Ho<sub>2sub>ScNbO<sub>7sub> synthesized at 1600 掳C: 3.8 脳 10<sup>鈭?sup> S/cm at 750 掳C, whereas in Sm system the highest bulk conductivity, 7.3 脳 10<sup>鈭?sup> S/cm at 750 掳C, is offered by the pyrochlore Sm<sub>2sub>ScTaO<sub>7sub> synthesized at 1400 掳C. In Sm<sub>2sub>ScTaO<sub>7sub> pyrochlore we have observed the first-order phase transformation at 鈭?50-700 掳C is related to rearrangement process in the oxygen sublattice of the pyrochlore structure containing B-site cations in different valence state and actually is absent in the defect fluorites.

The two holmium niobates show Curie-Weiss paramagnetic behavior, with the prevalence of antiferromagnetic coupling. The magnetic susceptibility of Sm<sub>2sub>ScTaO<sub>7sub> is a weak function of temperature, corresponding to Van Vleck paramagnetism.