Effects of temperature on conduction mechanism, ac electrical and dielectric properties of NdFe0.9Ni0.1O3 by employing impedance spectroscopy

Abstract

In the present work, the effects of temperature and frequency on the ac electrical and dielectric properties of polycrystalline NdFe0.9Ni0.1O3, prepared by solid-state reaction method, are investigated. From the impedance spectroscopic measurements, three relaxation processes are observed, which are related to grains, grain boundaries and electrode-semiconductor contacts in the measured temperature and frequency range. For NdFe0.9Ni0.1O3 sample, the applicable equivalent circuit model is (R g Q g)(R gb Q gb)(R c Q c) in the measured temperature range. Decrease in resistances and relaxation times of the grains and grain boundaries with temperature confirm the involvement of thermally activated conduction mechanisms. With the increase in temperature, the relaxation frequencies increase for all three processes and the conduction mechanism changes from Mott variable range hole hopping to adiabatic small polaronic hole hopping in this material. The permittivity of grains is from 8 to 10, while the high permittivity observed at higher temperatures is extrinsic (due to Maxwell-Wagner type polarizations), which is primarily due to the formation of different Schottky barriers. The grain boundaries, ceramic surfaces and electrode-semiconductor contacts mainly contribute in the colossal value of permittivity of NdFe0.9Ni0.1O3. The ac conductivity plots show the positive values of the ‘dσ/dT’ which indicate that the charge carriers are localized. The results of conductivity signify that the delocalization of charge carriers augment with increase in the temperature in this system.