OXIDE-ION CONDUCTION IN BA2IN2O5 AND BA3IN 2CEO8, BA3IN2HFO8, OR BA3IN2ZRO8

Oxide-ion conductivity in oxygen-deficient perovskites has been explored in two structures having ordered oxygen vacancies at room temperature. Ba2In2O5 was shown to be isostructural with Brownmillerite, Ba3In2MO8 (M = Ce, Hf, or Zr) with Ca3Fe2TiO8. Ba2In2O5 exhibits a low extrinsic O2--ion conductivity below 650-degrees-C, an intrinsic conductivity across an ordering energy gap DELTA-H(g) that decreases with increasing temperature in the interval 650-degrees-C < T < T(t), and a first-order transition to a fast oxide-ion conductor above T(t)almost-equal-to-930-degrees-C. The compounds Ba3In2Mo8 exhibit an extrinsic conductivity below 450-degrees-C that is markedly superior to that of the fluorite-related oxides, e.g. Gd-CeO2 and Y-ZrO2; in particular, Ba3In2ZrO8 has twice the dc conductivity at 400-degrees-C as CaZrO2 at 800-degrees-C. Disordering of the M4+ cations over the cation array and their preference for octahedral versus tetrahedral coordination introduces a disordering of the oxygen vacancies at lower temperatures. An extrinsic activation energy E(a)almost-equal-to-0.6 eV was found for Ba3In2ZrO8.