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

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$) phases; for example, with a fraction of 4\% and 96\% for the sample annealed at 1250\degree C. The particle morphology has altered from spherical (1000\degree C) to irregular-shaped (1250\degree C) as a result of increase in annealing temperature. The Raman spectroscopy, Fourier Transform Infrared spectroscopy and X-ray Photoemission Spectroscopy have been used to understand the vibrational and electronic properties. An optical band gap of 2.7~eV for the sample sintered at 1250\degree C is calculated using Ultraviolet-vis diffuse reflectance spectroscopy measurements. The dielectric studies shows the higher dielectric permittivity ($\hat{I}\mu$${}_r$) and lower dielectric loss for the sample annealed at 1250\degree C.

submitted