Impedance spectroscopy study and phase transition in phospho-vanadium mixed oxide LiZnV_0.5P_0.5O₄

Abstract

An X-ray crystallographic study has allowed us to identify a powder of the type LiZnV_0.5P_0.5O₄, which contains 50% of vanadium and 50% of phosphore, inside the binary system LiZnVO₄–LiZnPO₄. The structure is isotypic with the phenacite like LiZnP0₄. X-ray diffraction patterns are indexed according to the lattice parameters of the rhombohedral system and the R3 space group. IR spectra show the presence of VO₄ and PO₄ groups in the network of this material. The experimental results indicate that $\sigma_{\text{AC}}$($\omega$) is proportional to $\left( {\omega^{n} } \right)$. The activation energy found from the Arrhenius plot confirms that the conduction processing of the material is not due to simple hopping mechanism. The temperature dependence of frequency exponent n was investigated to understanding the conduction mechanism in LiZnV_0.5P_0.5O₄. The non-overlapping small Polaron tunneling (NSPT) model can explain the temperature dependence of the frequency exponent. A phase transition at T = 623 K has been evidenced by Differential scanning calorimetry (DSC) and subsequently confirmed by the analysis of dielectric and electric properties.