Electrical conductivity of Cs3PO4 doped with trivalent cations

Cs3 − 3xMxPO4 (M = Sc, Y, La, Sm, Nd) solid electrolytes have been synthesized, their phase composition has been determined, and their electrical conductivity has been measured as a function of temperature. In all of the systems, we have identified cesium orthophosphate based solid solutions. Above ∼550°C, the solid solutions are isostructural with the high-temperature, cubic phase of Cs3PO4. They offer high cesium ion conductivity owing to the formation of cesium vacancies via 3Cs+ → M3+ substitutions and the decrease in phase transition temperature. The conductivity of the synthesized solid solutions, (4.8−5.6) × 10−3 S/cm at 300°C and (1.6−1.9) × 10−1 S/cm at 800°C, is at the level of earlier studied Cs3 − 2xMxIIPO4 solid electrolytes.