Lattice dynamic and anomalous thermal transport of calcium sodium vanadates

Abstract

Calcium sodium vanadate compounds, including NaCaVO4 and Na2CaV4O12, have garnered significant interest for their extensive potential in various practical applications. Nonetheless, a comprehensive understanding of their intrinsic thermophysical properties remains elusive. Here, we present a comprehensive theoretical study on the lattice dynamic, thermodynamic properties, and thermal transport of NaCaVO4 and Na2CaV4O12. The thermodynamic properties including the heat capacity, thermal expansion coefficient, and Gibbs free energy over a wide range of temperatures are obtained. Moreover, utilizing the unified theory, we reveal the hierarchical thermal transport properties of NaCaVO4 and Na2CaV4O12, with diffusive channels making a significant contribution to the lattice thermal conductivity (κL). This contributes to the weak temperature dependence of κL, deviating from the typical κL ∼T-1 trend. With the consideration of normal and diffusive phonons, we predict the ultralow thermal conductivities of NaCaVO4 and Na2CaV4O12, which is derived from the bonding heterogeneity with the coexistence of weak Na-O (Ca-O) bonds and strong V-O bonds. This work offers crucial insights into the lattice dynamics and thermophysical characteristics of metal layered vanadates, potentially enhancing the utility of calcium sodium vanadate in various technological implementations.