Temperature dependence of electrical and thermal properties for perovskite-type rare earth cobalt oxide solid solutions Pr_1-xTb_xCoO₃ and their metal-insulator transition behavior

We prepared perovskite-type rare earth cobalt oxide solid solutions Pr_1-xTb_xCoO₃ (x = 0, 0.25, 0.5, 0.75, and 1) and investigated their metal-insulator transition behavior from the temperature dependence of electrical conductivity and specific heat. The solid solution exhibited cubic perovskite for x = 0 and 0.25 while orthorhombic phase was observed above 0.5, resulted in the distortion of CoO₆ octahedron. The metal-insulator transition temperature of Pr_1-xTb_xCoO₃ determined from both the electrical conductivity and specific heat measurements increased systematically with increasing x values. It is thus considered that the average ionic size of the R-site rare earth elements had an important role on the metal-insulator transition behavior and hence on the electrical properties. These results suggested that the metal-insulator transition temperature could be controlled by the chemical composition of the solid solutions of two type rare earth elements containing cobalt oxides.