Sintering, chemical stability and electrical conductivity of the perovskite proton conductors BaCe0.45Zr0.45M0.1O3−δ (M = In, Y, Gd, Sm)

The perovskite proton conductors BaCe0.45Zr0.45M0.1O3−δ (M = In, Y, Gd, Sm) containing equal molar proportions of both Ce and Zr were successfully synthesized by the conventional solid-state reaction route. The effect of sintering temperatures on phase purity, microstructure and electrical conductivity of these materials, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ac electrochemical impedance spectroscopy (EIS), respectively. In addition, chemical stability of the materials against CO2 at elevated temperatures and in boiling water was also investigated. The results indicate that 1600 °C is the optimum sintering temperature for maximizing conductivity. At 800 °C, the total conductivities of BaCe0.45Zr0.45M0.1O3−δ (M = In, Y, Gd, Sm) ceramics in air are 0.5 × 10−2, 1.06 × 10−2, 0.82 × 10−2 and 0.69 × 10−2 S cm−1, respectively. The activation energies are 79.8, 73.0, 71.6 and 66.5 kJ mol−1, respectively. While the conductivity of the mixed perovskite proton conductor decreases with increasing ionic radius from Y to Gd and Sm, there is an anomalous behaviour with respect to the smaller In dopant ion, giving rise to lowest conductivity in the above system. The ceramics are relatively stable in CO2; however, a small amount of amorphous phases can form in boiling water.