Conduction Mechanism and Dielectric Properties of Polycrystalline La0.53Ca0.47Mn0.5Cr0.5O3

Abstract

The electric conductivity and dielectric properties of polycrystalline La0.53Ca0.47Mn0.5Cr0.5O3 are studied with impedance spectroscopy techniques over a wide range of frequencies and temperatures from 100 to 1 MHz and 100 and to 400 K, respectively. The material exhibits a semiconductor behavior in the whole temperature range, characterized by a change in the slope at a specific temperature with a saturation at ~ 360 K. At low temperature, the conduction mechanism is governed by distributed trap localized charge carrier states described by a variable-range hopping model. At high temperature, the conduction mechanism is thermally activated by a small polaron hopping process. At low frequencies, the high dielectric constants of the material decrease rapidly with frequency and increase with temperature due to the free charges accumulated at the electrode-sample interface (interfacial Maxwell–Wagner polarization). These high dielectric constants can be interpreted by the existence of grain boundaries. Additionally, the Nyquist plots are presented by two depressed not centered semicircles on the real axis, indicating non-Debye behavior for the material. The resistance of the grain boundaries is larger than the resistance of the grains, confirming that the grain boundaries govern the conductivity in La0.53Ca0.47Mn0.5Cr0.5O3. Finally, the modulus analysis indicates a transition of carrier mobility from the long range in the low-frequency region to the short range in the high-frequency region.