Structurally modulated dielectric relaxation in rhombohedral Cr₂O₃ mediated by Mn addition

Abstract

A simple, energy and time efficient, sol–gel based auto-combustion route was employed to synthesize phase pure nanoparticles of Cr₂O₃ and MnCr₂O₄ to study structural, dielectric, impedance and ferroelectric properties. Crystal structure, identified through X-ray diffraction, revealed that Cr₂O₃ had rhombohedral symmetry (R-3c), while MnCr₂O₄ possessed cubic spinel symmetry with space group, Fd-3m. Data obtained from X-ray diffraction was further utilized to refine the diffraction patterns using Rietveld’s refinement approach to confirm the structural parameters. Frequency dependent dielectric properties have been investigated systematically in a high frequency range from 20 Hz to 20 MHz. Dielectric constant, loss factor and tangent loss were found to decrease with increase in frequency due to hopping and mainly explained on the basis of Maxwell–Wagner’s model followed by Koop’s theory. Impedance studies helped to define the electro-active regions and Nyquist plot thereby was used to evaluate grain and grain boundary resistance of the synthesized samples. Conductivity behavior followed by the typical Jonscher’s power law was confirmed by calculating the exponent in the expression and thus the hopping mechanism of charge carriers inside these chromites was studied. Ferroelectric analysis showed the potential of the synthesized samples in multifunctional memory devices, used in the miniaturized industry.