Development of proton conductors using pyrochlore-perovskite phase boundaries

The pyrochlore-perovskite binary systems La₂Zr₂O₇-SrZrO₃ and La₂Zr₂O₇-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 La₂Zr₂O₇ 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 La₂Zr₂O₇ was at least 0.25 mol fraction. Y-doped La₂Zr₂O₇ had the highest electrical conductivity, though no composition exceeded σ=3×10⁻⁴ S/cm at the target temperature of 600 °C. The effectiveness of Y as a dopant in La₂Zr₂O₇ was limited because Y substituted for both La on the A-site and Zr on the B-site. This paper was presented at the Fuel Cells: Materials, Processing, and Manufacturing Technologies Symposium sponsored by the Energy/Utilities Industrial Sector & Ground Transportation Industrial Sector and the Specialty Materials Critical Technologies Sector at the ASM International Materials Solutions Conference, October 13–15, 2003, in Pittsburgh, PA. The symposium was organized by P. Singh, Pacific Northwest National Laboratory, S.C. Deevi, Philip Morris USA, T. Armstrong, Oak Ridge National Laboratory, and T. Dubois, U.S. Army CECOM.