Impedance spectroscopic study of charge transport and relaxation mechanism in MnCr2O4 ceramic chromite

Abstract

In the present report, MnCr2O4 ceramic oxide has been prepared via the solution based self-combustion sol-gel route sintered at 900 °C. The Rietveld refinement of X-ray powder diffraction profile revealed the single-phase normal spinel structure of the ceramic crystallized in a face-centered cubic unit cell with Fd3m space group symmetry. The field emission scanning electron microscopy exposed well distribution of grains separated by grain boundaries as micro-constituents of the sample. Complex impedance spectroscopy deduced the distribution of relaxation times and thermal activation of charge carriers in the frequency and temperature ranges of 70−4×106 Hz and 543−643 K, respectively. The depressed semicircular arcs of the Nyquist plot modeled by an equivalent circuit with configuration RG׀׀CG+RGB׀׀CGB confirmed the bulk and interface contribution to the electrical response of the material. The correlated barrier hopping conduction addressed the temperature dependence of frequency exponent after simulation of the AC conductivity data by the equation of Jonscher. The complex modulus study identified the electro-active components of the material and determined the dominant role of grains in the conduction mechanism. The analysis of dielectric constant and loss factor stated thermally activated hopping mechanism of charge carriers between Cr2+ and Cr3+ ions at the octahedral sites of the crystal structure.