Comprehensive Study of Electronic, Optical, and Thermophysical Properties of Metavanadates CaV2O6 and MgV2O6

Calcium metavanadate (CaV2O6) and magnesium metavanadate (MgV2O6) have received considerable attention due to their great potential for many practical applications; however, a fundamental understanding of their intrinsic physical properties is still not well established. Here, we present a comprehensive experimental and theoretical study of the optical, electronic, and lattice dynamic properties of CaV2O6 and MgV2O6. We find that both compounds are semiconductors with indirect band gaps and exhibit visible light-emitting properties, which are thus expected to be the ideal candidates for phosphors or optoelectronic devices. Through density functional theory (DFT) calculations, we further show that CaV2O6 exhibits negative thermal expansion (NTE) below 80 K due to the flexible or intense coupled rocking of the CaO6 octahedra. Moreover, using the dual-phonon model, we disclose the hierarchical thermal transport features of these two compounds, in which diffusive channels make a significant contribution to the thermal conductivity κ, resulting in the weak temperature dependence of κ deviating from the typical κ ∼T–1 given by the phonon gas model. With the consideration of normal and diffusive phonons, we predict the ultralow and large anisotropic thermal conductivities of CaV2O6 and MgV2O6. This work provides a fundamental understanding of the optical, electronic, and thermal properties of metal-ion-intercalated layered vanadium oxides, which may promote the functional applications of metavanadates.