Improvement of grain-boundary conductivity of trivalent cation-doped barium zirconate sintered at 1600°C by co-doping scandium and yttrium

Scandium and yttrium co-doped barium zirconate [BaZr0.85 Scx Y0.15-x O3-δ (x=0, 0.05, 0.075, 0.10, 0.15)] have been investigated in terms of phase relationship, microstructures, and electrical conductivity. The bulk conductivity of the scandium and yttrium co-doped barium zirconate increased with the dopant ratio of yttria. BaZr0.85 Sc0.05 Y0.10 O3-δ had the highest grain-boundary conductivity among the scandium and yttrium co-doped barium zirconates in this study. But, BaZr0.85 Sc0.15 O3-δ, BaZr0.85 Sc0.10 Y0.05 O3-δ, BaZr0.85 Sc0.75 Y0.075 O3-δ, and BaZr0.85 Sc0.05 Y0.10 O3-δ consisted of a single cubic perovskite phase at 1600°C and their densities of grain-boundary were smaller than that of BaZr0.85 Y0.15 O3-δ. From the observation of microstructure and results of grain boundary-conductivity measurement, we can say that yttrium is a dopant that increases specific grain-boundary conductivity and bulk conductivity, and scandium is a dopant that increases the grain size. Thus, there is a trade-off relation between the grain size and specific grain-boundary conductivity based on the mixing ratio of scandia to yttria. The total conductivity of BaZr0.85 Sc0.05 Y0.10 O3-δ at 600°C was estimated to be 1.6× 10-2 S cm-1, which is the highest-class conductivity among reported trivalent cation-doped barium zirconates.