Conduction mechanism study by overlapping large-polaron tunnelling model in SrNiP2O7 ceramic compound

The SrNiP2O7 compound was prepared by a solid-state reaction method. Electrical properties and modulus analysis were studied using complex impedance spectroscopy in the frequency range 200 Hz-5 MHz and temperature range 609-728 K. The difference of the value of activation energy for the bulk obtained from analysis of equivalent circuit (0.88 eV) and modulus relaxation (0.77 eV) confirms that the transport is not due from a simple hopping mechanism. The AC conductivity is studied using the following equation: sigma(ac)(omega) = sigma(s)/1+tau(2)omega(2) + sigma(infinity)tau(2)omega(2)/1+tau(2)omega(2) + A omega(s). The temperature dependence of the power law exponent s and a.c conductivity sigma(ac) is reasonably interpreted by the overlapping large polaron tunneling (OLPT) model. The mechanism of conduction is probably due from the displacements of the Sr2+ ion in the tunnel-type cavities along the a and b axis. (C) 2013 Elsevier B. V. All rights reserved.