Microstructural characterization and electrical properties of spray pyrolyzed conventionally sintered or hot-pressed BaZrO3 and BaZr0.9Y0.1O3 − δ

A spray pyrolysis route to BaZrO3 (BZ) and BaZr0.9Y0.1O2.95 (BZY) powders was developed starting from nitrate solutions. Homogeneous powders with a grain size of ~ 100 nm were achieved. A calcination of the powder was necessary to remove carbonates formed during the spray pyrolysis. Hot pressing was in comparison with conventional sintering more effective to enhance densification and suppress grain growth, and dense (> 96%) materials with homogeneous microstructure were obtained. The Y-substitution decreased the densification rate. Minor amounts of a secondary phase was observed at the grain boundary triple points of BZY, but the grain boundaries were otherwise found to be coherent and without significant secondary phase accumulation. Impedance spectroscopy vs T, pO2 and pH2O of conventionally sintered BZ and hot-pressed BZY demonstrated that the conductivity of BZ was orders of magnitude lower than compared to BZY. The conductivity of BZ displayed mixed proton and p-type electronic conduction characteristics in the grain interior which was depressed at the grain boundaries. The grain boundaries showed an additional n-type electronic conduction under reducing conditions. The conductivity characteristics were according to core-space charge layer theory. BZ seems to exhibit a larger ratio of p-type electronic to protonic conduction as compared to BZY, contrary to the prediction of simple defect chemistry.

Research Highlights
► A spray pyrolysis route to BaZrO3-based powders has been developed.
► Hot pressing gave fine-grained materials with homogeneous microstructure.
► The conductivities were explained to core-space charge layer theory.
► BZ exhibits a higher p-type electronic to protonic conduction as compared to BZY.