Temperature dependent AC-Conduction and relaxation mechanism of spinel MgCo 2 O 4 system by impedance spectroscopy

摘要

MgCo2O4 a spinel ceramic was studied by complex impedance spectroscopy. The measurements were performed in the temperature and frequency ranges 83 to 323 K and 40 Hz to 1 MHz, respectively. The decreasing trend in Nyquist plots semicircles was observed as a function of temperature indicating the distribution of different relaxaion processes. Two equivalent circuit models (RgCg)(RgbQgb) below 173 K and above this temperature (Rg) (RgbQgb) were applied to fit the impedance data. The values obtained for Rgb and Rg from these model fitting displayed semiconducting like behavior in the material. The variable range hopping model was employed to explain electrical conduction mechanism of grains and grain-boundaries. The complex modulus analysis asserted the contribution of both bulk and grain boundaries in electrical conductivity at low temperatures. The frequency dependent ac-conductivity followed the universal Jonscher's power law. The frequency exponent n showed a decreasing trend with increasing temperature. The ac-conductivity data was further elaborated by Correlated Barrier Hopping Model (CBH).