Comprehensive Study of Electronic, Optical, and Thermophysical Properties of Metavanadates CaV <subscript>2</subscript> O <subscript>6</subscript> and MgV <subscript>2</subscript> O <subscript>6</subscript> .

Calcium metavanadate (CaV 2 O 6 ) and magnesium metavanadate (MgV 2 O 6 ) 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 CaV 2 O 6 and MgV 2 O 6 . 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 CaV 2 O 6 exhibits negative thermal expansion (NTE) below 80 K due to the flexible or intense coupled rocking of the CaO 6 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 CaV 2 O 6 and MgV 2 O 6 . 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.