Physical and Dielectric Properties of Polycrystalline LaV$_{0.5}$Nb$_{0.5}$O$_4$

TL;DR

This study investigates the structural, vibrational, electronic, and dielectric properties of polycrystalline LaV$_{0.5}$Nb$_{0.5}$O$_4$, revealing phase coexistence, morphological changes, and improved dielectric performance with higher annealing temperature.

Contribution

It provides new insights into how Nb substitution and annealing temperature affect the phases, morphology, and dielectric properties of LaV$_{0.5}$Nb$_{0.5}$O$_4$.

Findings

Coexistence of monoclinic and tetragonal phases confirmed by XRD.

Higher annealing temperature increases dielectric permittivity.

Optical band gap of 2.7 eV for the sample sintered at 1250°C.

Abstract

We report a detailed investigation of the structural, electronic, vibrational, and dielectric properties of polycrystalline LaV$_{0.5}$Nb$_{0.5}$O$_4$ samples, prepared at two sintering temperatures (1000\degree C and 1250\degree C). The introduction of Nb$^{5+}$ at the V$^{5+}$ site leads to notable structural and vibrational changes, which can be attributed to their isoelectronic nature and the comparatively larger ionic radius of Nb$^{5+}$. The Rietveld refinement of the X-ray diffraction patterns confirms a coexistence of monoclinic ($P$2$_{1}$/$n$) and scheelite-type tetragonal ($I$4$_{1}$/$a$) phases; for example, with a fraction of 4\% and 96\% for the sample annealed at 1250\degree C. The particle morphology has altered from spherical (1000\degree C) to irregular-shaped (1250\degree C) as a result of increase in annealing temperature. The Raman spectroscopy, Fourier Transform Infrared spectroscopy and X-ray Photoemission Spectroscopy have been used to understand the vibrational and electronic properties. An optical band gap of 2.7~eV for the sample sintered at 1250\degree C is calculated using Ultraviolet-vis diffuse reflectance spectroscopy measurements. The dielectric studies shows the higher dielectric permittivity ($\epsilon$$_{r}$) and lower dielectric loss for the sample annealed at 1250\degree C.