Bonding Inhomogeneity and Strong Anharmonicity Induce Ultralow Lattice Thermal Conductivity in Calcium Pyrovanadate

Calcium pyrovanadate (Ca2V2O7) has been reported as an advanced functional material for optoelectronics and energy storage owing to its layered crystal structure and intense O2-V5+ charge transfer bands. Therefore, the studies on the physicochemical properties of Ca2V2O7 to further improve its service performance are indispensable. Herein, we systemically investigate the structural, lattice dynamic, and thermodynamic properties of Ca2V2O7 utilizing experimental measurements and first-principles calculations. The measured heat capacity is found to obviously break through the Dulong-Petit limit, indicating that strong anharmonicity is present in Ca2V2O7. Furthermore, we reveal the hierarchical thermal transport behavior of Ca2V2O7 in the dual-phonon theory framework and predict the ultralow lattice thermal conductivity (kappa) with values of 2.15, 2.11, and 1.91 W/ mK along the a, b, and c axes at 300 K. The results indicate that a significant contribution from diffusive thermal transport to the. is observed, leading to a temperature-dependent. much flatter than that of the general law of kappa similar to T-1 in most other materials. This study not only promotes the diverse applications of Ca2V2O7 such as thermal insulating materials and batteries but also provides novel insights into the fundamental thermal physics of calcium-intercalated layered vanadium-based oxides.