Improvement of grain-boundary conductivity of trivalent cation doped barium zirconate

The sintering behavior of 15% scandium or yttrium doped barium zirconate (BaZr_0.85Sc_0.15O_3-δ or BaZr _0.85Y_0.15O_3-δ) was investigated. Large and uniform grains were observed in 15% scandium-doped barium zirconate by sintering for 24 hours. This is because the phase relationship of 15% scandium-doped barium zirconate does not change between 1300 and 1600 °C. In contrast, typical microstructures of 15% yttrium-doped barium zirconate sintered for between 4 and 24 hours at 1600 °C were bimodal. This is because the phase relationship of 15% yttrium-doped barium zirconate changes between 1300 and 1600 °C. It takes a long time to obtain large and uniform grains of BaZr_0.85Y_0.15O_3-δ. Also, scandium and yttrium co-doped barium zirconate (BaZr_0.85Sc_xY _0.15-xO_3-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. As for grain-boundary conductivity, BaZr_0.85Sc_0.05Y_0.10O _3-δ had the highest grain-boundary conductivity among the scandium and yttrium co-doped barium zirconates in our study. From the observation of microstructure and results of grain boundary-conductivity measurement, we can say that yttrium is a dopant which increases specific grain-boundary conductivity and bulk conductivity, and scandium is a dopant which increases the grain size. Thus, there is a trade-off relationship between the grain size and specific grain-boundary conductivity based on the mixing ratio of scandium to yttrium.