Exploring the Sm1鈥搙CaxF3鈥搙 Tysonite Solid Solution as a Solid-State Electrolyte: Relationships between Structural Features and F鈥?Ionic Conductivity

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• 作者：Belto Dieudonn茅 ; Johann Chable ; Fabrice Mauvy ; Sebastien Fourcade ; Etienne Durand ; Eric Lebraud ; Marc Leblanc ; Christophe Legein ; Monique Body ; Vincent Maisonneuve ; Alain Demourgues
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：November 12, 2015
• 年：2015
• 卷：119
• 期：45
• 页码：25170-25179
• 全文大小：591K
• ISSN：1932-7455

文摘

Pure tysonite Sm_1鈥?i>xCa_xF_3鈥?i>x solid solutions for 0.05 鈮?x 鈮?0.17 have been prepared by the solid-state route. For the first time, the partial Sm_1鈥?i>xCa_xF_3鈥?i>x solid solution is investigated on the basis of structural features and ionic conductivity measurements. Powder X-ray diffraction Rietveld refinements show an unexpected decrease of the hexagonal unit cell volume related to the creation of fluorine vacancies. The local environment of F1, which is mainly responsible for the ionic conductivity, changes with the Ca content: the distortion of the F1(Sm,Ca)₄ tetrahedral site decreases with the Ca content. Fluoride ion exchanges have been qualitatively probed on two Sm_1鈥?i>xCa_xF_3鈥?i>x (x = 0.05 and x = 0.15) samples thanks to ¹⁹F magic angle spinning NMR experiments at various spinning frequencies and temperatures. At room temperature, the ionic conductivity decreases exponentially with the Ca content and the activation energy increases monotonously with the Ca content. The highest conductivity is found for the lowest Ca content or the smallest fluorine vacancy content stabilized in the Sm_1鈥?i>xCa_xF_3鈥?i>x tysonite network corresponding to Sm_0.95Ca_0.05F_2.95 (10^鈥? S路cm^鈥?, E_a = 0.36 eV at room temperature). For this composition, the largest dispersions of F2鈥?Sm,Ca) and F3鈥?Sm,Ca) distances as well as (Sm,Ca)鈥揊1鈥?Sm,Ca) angles are observed. The buckling of F2/F3 sheets around the z = 1/4 coordinate for low Ca content affects the large F1 tetrahedral site with the strongest distortion. The higher the buckling effect into the F2/F3 sheets, the higher the F1 local site distortion and the higher the ionic mobility and conductivity.