Melting/collapse of charge orbital ordering and spread of relaxation time with frequency in La0.50Ca0.50MnO3+δ by impedance spectroscopy

Abstract

Impedance spectroscopy has been employed to investigate the microscopic nature of the charge/orbital ordering (COO) in polycrystalline La0.50Ca0.50MnO3+δ sample at different temperatures. The modulations of relaxation time with temperatures show different behaviors of Z′ and Z″. An equivalent circuit model (R1C)(R2Q) has been employed to investigate the electrical parameters of La0.50Ca0.50MnO3+δ at different temperatures. The resistance of grain and grain boundaries shows maxima at metal-insulator (MI) transition temperature (≈153 K). Three temperature zones have been identified. In the first temperature zone which has been from 85 to 140 K, below MI transition temperature, melting of COO with strong Jahn–Teller (JT) distortions has been reported. In the second zone, around MI transition temperature, melting and collapse of COO with weak JT distortion result in colossal drop in Z′. In the third temperature zone, above MI transition temperature, charge ordering (CO) around 203 K and onset of short range CO at 253 K have been determined.