Correlated barrier hopping transport and non-Debye type dielectric relaxation in Zn2V2O7 pyrovanadate

Abstract

Herein, the Zn₂V₂O₇ electro-ceramic pyrovanadate was synthesized via a conventional solid-state reaction technique and calcined at 700 °C. The single phase formation of Zn₂V₂O₇ pyrovanadate crystallized in the monoclinic structure with C12/c1 space group was confirmed by X-ray diffraction (XRD). The XRD powder diffraction profile was analyzed by Rietveld refinement to investigate the structural details of the compound. The complex impedance analysis was carried out in the frequency domain of $83-2\times {10}^6$ Hz over a temperature range of 453–613 K to study the electrical charge conduction and dielectric relaxation mechanism in the material which revealed the presence of the distribution of relaxation times with thermal charge activation. Depressed semicircles in the Nyquist plots were modeled by an equivalent circuit with configuration (R_GC_G)(R_GBQ_GB) which resolved the contributions of grains and grain boundaries towards the transport properties of the material. The electrical conductivity spectra followed Jonscher's power law behavior and the temperature variation of frequency exponent suggested correlated barrier hopping (CBH) as the governing transport mechanism in the Zn₂V₂O₇ pyrovanadate system. The comparison between scaling behaviors of imaginary parts of impedance and modulus advocated the temperature-independent nature of relaxation time distribution. The imaginary electrical modulus spectra were reproduced by the Kohlrausch, Williams, and Watt formulism, and the fitted parameters confirmed the non-Debye type nature of the dielectric relaxation. Further, the Haveriliak-Negami function was employed to investigate the dielectric response of the material which was found to be consistent with impedance, conductivity, and modulus analyses. The frequency dispersion of the tangent loss verified that the hopping mechanism was thermally activated.