Metal-Insulator Phase Transition and Structural Stability in ‘Sb’ Doped CaMnO3 Perovskite

Abstract

Electron doped Ca1-xSbx MnO3 (X = 0 to 0.4) compound when prepared by high temperature solid state reaction, exhibits orthorhombic distorted perovskite structure. A systematic, continuous doping increases the metal – insulator transition temperature to above the room temperature (≈431 to 469 K); due to the mismatch of ionic radii in A site rising anti - site effect, which consequently changes the bond length. Doping induced metal – insulator transition accompanied by structural transition is reflected through the drastic changes in the parameters like cation size variance factor (), average ionic radius <r>, tolerance factor (t) and To-which is correlated to the band related transport properties. Structural transition from the phase of perovskite to Brownmillerite has been found for the compositions x = 0.3 and 0.4, which is attributed due to the ionic radii mismatch. Doping exerts chemical pressure by modifying compression of A-O bond and relaxation of B-O bond, giving rise to strain similar to external pressure in ABO3 perovskite. The dependence of electrical transport at high temperature has been studied, by employing variable range hopping and small polaron hopping model as an account for the experimental observation due to disorder induced localization.