Electronic structure and electrical conduction by polaron hopping mechanism in A2LuTaO6 (A= Ba, Sr, Ca) double perovskite oxides

Impedance spectroscopy has been applied to explore electrical properties of polycrystalline double perovskite oxides A2LuTaO6 (A = Ba, Sr, Ca; ALT). The phase purity and microstructural analysis of the samples are obtained from XRD and SEM. Ba2LuTaO6 (BLT) crystallizes in a single phase whereas in Sr2LuTaO6 (SLT) and Ca2LuTaO6 (CLT) a small secondary phase of Lu2O3 was detected. The Nyquist plots for ALT reveals the rising dominance of the grain boundary contribution to the conduction process with increasing temperature. The complex modulus plots confirm the presence of both the grain and grain boundary contributions to the relaxation process at low temperatures. The relaxation mechanism is seen to be shifted from its ideal character as observed in the Nyquist plots. The frequency dependent conductivity spectra follow the power law behavior. Small polaron hopping is responsible for the electrical conduction in these materials in the entire temperature range. Density functional theory calculations are performed to understand the electronic structure of the materials. The density of states (DOS) for BLT, SLT and CLT establishes the semiconducting ground state of the materials. The conductivity mechanism is analysed on the basis of the calculated DOS.