Effects of ZnO addition methods on proton conductivities of barium zirconate modified by ytterbium

Yb-doped BaZrO3 samples with relative densities higher than 98% were obtained by the addition of 4 mol% stoichiometric ZnO, excess ZnO, and excess BaZnO2, and sintering at 1300 °C for 10 h. The stoichiometric addition of ZnO was most effective in obtaining a homogeneous distribution of Zn throughout the grains and grain boundaries. The Yb-doped BaZrO3 obtained using a stoichiometric addition of ZnO had the cubic perovskite structure, whereas the others had monoclinic perovskite structures. The highest proton conductivity was obtained when ZnO was added stoichiometrically; the conductivity of Yb-doped BaZrO3 with stoichiometric ZnO and excess ZnO at 500 °C was 0.0012 Scm− 1 and 0.0004 Scm− 1, respectively. The results are discussed from the viewpoint of the crystal structure and the defect chemistry.