Development of Proton Conductors Using Pyrochlore-Perovskite Phase Boundaries

The pyrochlore-perovskite binary systems La^sub 2^Zr^sub 2^O^sub 7^-SrZrO3 and La^sub 2^Zr^sub 2^O^sub 7^-LaYO3 were studied as potential high-temperature proton conductors. X-ray diffraction and direct current conductivity measurements were used to develop empirical relationships between structure and conductivity. The solubilities of Sr in La^sub 2^Zr^sub 2^O^sub 7^ and La in SrZrO3 were low, less than 0.1 mol fraction. The solubility of Zr in LaYO3 was at least 0.125 mol fraction, and the solubility of Y in La^sub 2^Zr^sub 2^O^sub 7^ was at least 0.25 mol fraction. Y-doped La^sub 2^Zr^sub 2^O^sub 7^ had the highest electrical conductivity, though no composition exceeded σ=3×10^sup -4^ S/cm at the target temperature of 600 °C. The effectiveness of Y as a dopant in La^sub 2^Zr^sub 2^O^sub 7^ was limited because Y substituted for both La on the A-site and Zr on the B-site.[PUBLICATION ABSTRACT]