Observation of semiconductor to metallic transition and polaron hopping in double perovskite Pr2CoTiO6 ceramics

This paper describes semiconductor to metal transition and polaron conduction in double perovskite Pr2CoTiO6 (PCTO) ceramics. The XRD pattern recorded at room temperature confirmed the pure phase, single crystalline structure. The semicircle arc in the impedance plot at each temperature can be attributed to the grain boundary contribution, indicating one dominating response in the measurement frequency range. The semiconductor to metallic transition was also confirmed by the variation of grain boundary resistance (Rgb) with temperature. The activation energy estimated from the imaginary part of electrical modulus and impedance are found to be the characteristic of polaron conduction in PCTO. Ac conductivity followed power law dependence σac = Bωn. The observed variation of the exponent 'n' with temperature suggests the typical of charge transport assisted by a hopping process. The observed minimum in the temperature dependence of frequency exponent 'n' strongly suggests that the large polaron tunneling is the dominant transport process.