High-temperature protonic conduction in LaP₃O₉

A novel proton-conducting material based on LaP₃O₉ was developed and its electrical conduction properties were investigated by measuring conductivities under 0.4-5 kPa of p(H₂O) and 0.01-100 kPa of p(O₂) at 573-973 K. LaP₃O₉ conducted protons dominantly by partial substitution of Sr for La. Conductivities of the 1 mol % Sr-doped LaP₃O₉ were 7 × 10^-7 to 3 × 10^-4 S cm^-1 at 573-973 K, and were relatively higher than those of other proton-conducting rare earth phosphates such as LaPO₄ and La₇P₃O₁₈. Conductivities of the Sr-doped LaP₃O₉ were almost independent of p(H ₂O), suggesting dominant protonic conduction even under low p(H ₂O) conditions.