High-temperature protonic conduction in LaBO₃ substituted with alkaline earth elements

Abstract

Electrical conduction properties of the aragonite-type LaBO₃-based materials, in which La was substituted partially by Ca, Sr and Ba, were investigated at 500–925°C with conductivity and transport-number measurements. From X-ray diffraction measurements, it was confirmed that a solubility limit of Sr to the La site is between 1 and 2 mol %. When the substitution content exceeded the solubility limit, the conductivities decreased with increasing the concentration. Such a deterioration in the conductivity was considered to be resulted from an impurity-phase formation. Regardless of substitution species, the LaBO₃ exhibited predominant protonic conduction by the partial substitution of the alkaline earth elements for La, and the Sr-substituted sample showed the highest conductivities. The proton transport numbers were estimated as 0.7–0.9 from electromotive forces of water-vapor and oxygen concentration cells.