Anomalous Lattice Behavior of Vanadium Pentaoxide (V2O5): X- Ray Diffraction, Inelastic Neutron Scattering and ab-initio Lattice Dynamics

TL;DR

This study investigates the anisotropic thermal expansion and lattice dynamics of layered V2O5 using X-ray diffraction, neutron scattering, and ab-initio calculations, revealing anomalous behaviors and insights into phase stability.

Contribution

It provides a comprehensive analysis of V2O5's lattice behavior, highlighting the roles of van der Waals forces and Hubbard interactions, and clarifies discrepancies with previous TEM and EELS studies.

Findings

Anisotropic and anomalous thermal expansion observed from 12 K to 853 K.

No evidence of structural phase transition or decomposition in the studied temperature range.

Softening of elastic constant C66 indicates potential shear-driven phase transformation.

Abstract

We present the structural and dynamical studies of layered vanadium pentaoxide (V2O5). The temperature dependent X-ray diffraction measurements reveal highly anisotropic and anomalous thermal expansion from 12 K to 853 K. The results do not show any evidence of structural phase transition or decomposition of {\alpha}-V2O5, contrary to the previous transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) experiments. The inelastic neutron scattering measurements performed up to 673 K corroborate the result of our X-ray diffraction measurements. The analysis of the experimental data is carried out using ab-initio lattice dynamics calculation. The important role of van der-Waals dispersion and Hubbard interactions on the structure and dynamics is revealed through the ab-initio calculations. The calculated anisotropic thermal expansion behavior agrees well with temperature dependent X- ray diffraction. The mechanism of anisotropic thermal expansion and anisotropic linear compressibility is discussed in terms of calculated anisotropy in Gr\"uneisen parameters and elastic coefficients. The calculated Gibbs free energy in various phases of V2O5 is used to understand the high pressure and temperature phase diagram of the compound. Softening of elastic constant (C66) with pressure suggests a possibility of shear mechanism for {\alpha} to \b{eta} phase transformation under pressure.