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

Scandium and yttrium co-doped barium zirconate [BaZr(0.85)Sc(x)Y(0.15-x)O(3-delta) (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. BaZr(0.85)Sc(0.05)Y(0.10)O(3-delta) had the highest grain-boundary conductivity among the scandium and yttrium co-doped barium zirconates in this study. But, BaZr(0.85)Sc(0.15)O(3-delta), BaZr(0.85)Sc(0.10)Y(0.05)O(3-delta), BaZr(0.85)Sc(0.75)Y(0.075)O(3-delta), and BaZr(0.85)Sc(0.05)Y(0.10)O(3-delta) consisted of a single cubic perovskite phase at 1600 degrees C and their densities of grain-boundary were smaller than that of BaZr(0.85)Y(0.15)O(3-delta). 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 BaZr(0.85)Sc(0.05)Y(0.10)O(3-delta) at 600 degrees C was estimated to be 1.6x10(-2) S cm(-1), which is the highest-class conductivity among reported trivalent cation-doped barium zirconates. (C) 2008 The Electrochemical Society.