Conductivity of Co and Ni doped lanthanum-gallate synthesized by citrate sol–gel method

Solid solutions of Sr and Mg doped lanthanum-gallate (LSGM) with addition of 3 and 5at% of cobalt and nickel at the B-site in ABO3 perovskite structure were obtained using citrate sol–gel method. The synthesized powders were calcined at 900°C and then finally sintered at 1450°C for only 2h, which resulted in approximately 95% density. Impedance spectroscopy was utilized for electrical characterization in the temperature range 200–600°C. The activation energies calculated from impedance spectra for bulk and grain boundary conductivities were decreased by the addition of transition metals (Co and Ni) and subsequently the conductivity was increased. Two different regions were clearly distinguished in the plots ln(σT) vs. 10,000/T for grain boundary conductivities, indicating changes in the mechanism of charge transport with the temperature. It is concluded that addition of cobalt above 5at% in the LSGM prepared by citrate sol–gel method does not enhance the electrolytic properties of LSGM. XRD results suggested possible coexistence of two perovskite crystalline phases in nickel doped samples. However, it is still more favorable for use in IT-SOFC applications than cobalt since it has less influence on the electrolytic domain of LSGM.