Small polaron hopping transport mechanism, dielectric relaxation and electrical conduction in NiAl2O4 electro-ceramic spinel oxide

Abstract

In this study, the frequency and temperature dependent dielectric relaxation and electrical conduction mechanisms in NiAl2O4 spinel oxide ceramic have been explored in a frequency range of over a measured temperature from 163–283 K. The polycrystalline NiAl2O4 was synthesized via solid state reaction route and sintered at 1000 °C. The room temperature x-ray powder diffraction pattern confirmed the formation of NiAl2O4 spinel phase with Fd3m space group. The surface morphology of the sample was investigated by scanning electron microscopy and chemical properties by Fourier transform infrared spectroscopic analysis. Complex impedance studies revealed the presence of relaxation time distribution and charge carriers were found to be thermally activated. The Nyquist plots exhibited depressed semicircles and their fitting by an equivalent circuit model with configuration (RGCG)(RGBCGB) resolved the contributions of grains and grain-boundaries to the electrical transport properties of the material. Electrical conductivity analysis followed the Jonscher’s power law behavior and the frequency exponent suggested small polaron hopping as the governing transport mechanism in NiAl2O4 spinel oxide. Non-Debye type nature of dielectric relaxation was confirmed by the complex modulus analysis whereas dielectric constant and tangent loss analysis verified that the hopping mechanism was thermally activated.