Vanadium Oxides: Synthesis, Properties, and Applications

Abstract

Correlated electrons in vanadium oxidesVanadium oxidesare responsible for their extreme sensitivity to external stimuli such as pressure, temperature, or doping. As a result, several vanadium oxidesVanadium oxidesundergo insulator-to-metal phase transition (IMT) accompanied by structural change. Unlike vanadium pentoxide (V2O5)Vanadium pentoxide (V2O5), vanadium dioxide (VO2)Vanadium dioxide (vo2)and vanadium sesquioxide (V2O3)Vanadium sesquioxide (V2O3)show IMT in their bulk phases. In this study, we have performed one-electron Kohn--Sham electronic band structureStructurecalculations of VO2, V2O3, and V2O5 in both metallic and insulating phases, implementing a full Ab initio simulation package based on Density Functional Theory (DFT)Density Functional Theory (DFT), plane waves, and pseudopotentialsPseudopotentials(PPs). Electronic band structuresBand structuresare found to be influenced by crystal structureStructure, crystal field splittingCrystal field splitting, and strong hybridization between O2p and V3d bands. ``Intermediate bands'' with narrow bandwidths, lying just below the higher conduction bands, are observed in V2O5 which play a critical role in optical and thermoelectric processes. Similar calculations are performed for both metallic and insulating phases of bulk VO2 and V2O3. Unlike in the metallic phase, bands corresponding to ``valence electrons'' considered in the PPs are found to be fully occupied in the insulating phases. Transport parameters such as Seebeck coefficient, electrical conductivityElectrical conductivity, and thermal (electronic) conductivity are studied as a function of temperature at a fixed value of the chemical potential close to the Fermi energy using Kohn--Sham band structureBand structureapproach coupled with Boltzmann transport equations. Because of the layered structureStructureand stability, only V2O5 shows significant thermoelectric propertiesThermoelectric properties. All the transport parameters have correctly depicted the highly anisotropic electrical conduction in V2O5. Maxima and crossovers are also seen in the temperature-dependent variation of Seebeck coefficient in V2O5, which can be consequences of ``specific details'' of the band structureBand structureand anisotropic electron--phonon interactions. For understanding the influence of phase transition on transport propertiesTransport properties, we have also studied transport parameters of VO2 for both metallic and insulating phases. The Seebeck coefficient, at experimental critical temperature of 340 K, is found to change by 18.9 {\textmu}V/K during IMT, which lies within 10% of the observed discontinuity of 17.3 {\textmu}V/K. Numerical methods have been used to analyze the optical propertiesOptical propertiesof bulk and thin films of VO2, V2O3, and V2O5, deposited on Al2O3 substrates from infrared to vacuum ultraviolet range (up to 12 eV). The energies corresponding to the peaks in the reflectivity-energy (R-E) spectra are explained in terms of the Penn gap and the degree of anisotropy is found to be in the order of V2O3{\thinspace}