INVESTIGATIONS ON BATH0.9GD0.1O3 AS AN INTERMEDIATE TEMPERATURE FUEL-CELL SOLID ELECTROLYTE

The perovskite solid electrolyte BaTh0.9Gd0.1O3 incorporated into fuel cells possessing the general configuration H2(3% H2O) Pd/BaTh0.9Gd0.1O3/La0.9Sr0.1CoO3 (3% H2O), O2 has been studied. Ionic conductivity was found to progressively increase by congruent-to 30% upon passage of current through cells for over a day, with values up to 8.7 x 10-2 S cm-1 being found at 550-degrees-C. During this same time, activation energy (E(a)) for ionic transport decreased from congruent-to 0.6 eV to congruent-to 0.4 eV and appeared to coincide with a lattice phase change from cubic to orthorhombic. This latter observation may have been a consequence of introduced lattice protons during fuel cell operation. E(a) for ionic conduction was in general agreement with predictions between E(a) and calculated lattice 'free volumes' for this material. Evidence suggests this solid electrolyte to be predominantly a proton conductor at intermediate temperatures.