Impedance spectroscopic investigation of delocalization effects of disorder induced by Ni doping in LaFeO3

Polycrystalline LaFe1-xNixO3 (x = 0.0, 0.1, 0.3 and 0.5) oxides are prepared by a solid-state reaction method. In order to explore the delocalization effects of disorder induced by Ni substitution, dependence of the ac electrical properties of the synthesized composition is investigated in a wide temperature (77-300 K) and frequency (1-10 MHz) range by impedance spectroscopy. Room temperature near-edge x-ray absorption fine structure experiment at O K edge is performed to probe the unoccupied density of states. Grain boundaries play a dominant role in determining the resistive properties of the series. These systems are semiconducting and the origin of their semiconducting nature changes with Ni doping. At low doping levels (x <= 0.3) the semiconducting nature is dominated by an increase in mobility of the localized charge carriers, which hop between their localized states. For x = 0.5, the semiconducting nature is determined by an increase in carrier density. These results are explained in terms of a metallic conduction band formed by the hybridization of O 2p and Ni 3d orbitals.