Electrochemical properties of Cs-substituted CaWO₄ and BaWO₄ oxide ion conductors

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High-temperature electrochemical properties of Cs-substituted CaWO₄ and BaWO₄ have been investigated. When cesium ions are partly substituted for calcium site of Scheelite-type structured CaWO₄ to form oxide ion vacancies as Ca_1−xCs_xWO_4−x/2, oxide ion conduction appears at elevated temperatures. This defect structure for the oxide ion conduction is in contrast to the PbWO₄-based oxide ion conductor with oxide ion interstitials, Pb_1−xLa_xWO_4+x/2. The measured electric conductivity of Ca_1−xCs_xWO_4−x/2 (x = 0.15) is high as 10⁻² Scm⁻¹ at 750°C with the oxide ion transport number relatively close to unity. Essentially the similar results are obtained for the barium analogous system Ba_1−xCs_xWO_4−x/2, although the conductivity is still lower than CaWO₄-based system.