Dependence of dopant cations on microstructure and proton conductivity of barium zirconate

The effects of various cations (Mg2+, In3+, Yb3+, Tm3+, Er3+, Ho3+, Gd3+, Nd3+, La3+, Bi3+, and Ga3+) were examined as dopants into the B site of perovskite barium zirconate. The solubility of In, Yb, Tm, Er, and Ho, whose ionic radii are close to that of zirconium ion, into the B site is more than 0.075 (XMO1.5 =0.075) at 1600°C. In contrast, when there is a large difference of ionic radii between trivalent cations (Nd3+, La3+, Bi3+, and Ga3+) and zirconium ion, the solubility of trivalent cations into barium zirconate is less than XMO1.5 =0.075. The microstructure of sintered pellets and their conductivity in wet atmosphere were investigated. We could divide dopants into two classes based on the extent of proton conductivity and microstructure: "Y-type" and "Sc-type" dopants. Yb, Ho, Er, and Tm belong to Y-type dopants, which have a microstructural mixture of coarse and fine grains and higher proton conductivity. In belongs to Sc-type dopants, which have well-grown grains and lower proton conductivity.