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DOI: 10.1039/A900999J (Paper) Reference Section for: J. Mater. Chem., 1999, 9, 1357-1362

New cation conducting solid electrolytes with the Sc2(WO4)3 type structure

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Joachim Köhler, Nobuhito Imanaka and Gin-ya Adachi

Abstract

The Sc2(WO4)3 type structure has been used in order to create new trivalent cation conducting solid electrolytes by forming solid solutions of the type (Sc2(WO4)3)1–x(M2(MoO4)3)x (M=Nd, Sm, Gd, Lu). In these compounds, the anionic part of the structure is partly replaced by molybdate (WO4→MoO4) whereas the Sc3+ cations are substituted by different larger lanthanide cations M (Sc→M). Increasing the size of M gradually leads to a restriction of the M2(WO4)3 solubility in the scandium tungstate phase (e.g., x=0-1 for M=Lu but x=0-0.1 for M=Nd). The electrical properties of the resulting materials have been characterized in detail. All solid solutions exhibit neither electronic nor anionic O2– conduction but rather a mixed trivalent Sc3+/M3+ cationic conduction with the Sc3+ cations as the main charge carrying species for low M2(MoO4)3 concentrations (x<0.5) and the ionic transference number is >99%. For a given substitution rate of M for Sc, the electrical conductivity increases with increasing size of M. The highest conduction data were observed for the solid solution (Sc2(WO4)3)0.75(Sm2(MoO4)3)0.25 exhibiting a conductivity of 2.4×10–4 S cm–1 at 600[thin space (1/6-em)]°C with an activation energy of 45.8 kJ mol–1. Furthermore, in all different systems the maximum conductivity appears for the same average trivalent cationic radius indicating an optimized spatial spacing for the mobile cationic species.

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