Low thermal conductivity in a modular inorganic material with bonding anisotropy and mismatch

Abstract

The thermal conductivity of crystalline materials cannot be arbitrarily low as the intrinsic limit depends on the phonon dispersion. We used complementary strategies to suppress the contribution of the longitudinal and transverse phonons to heat transport in layered materials containing different types of intrinsic chemical interface. BiOCl and Bi₂O₂Se encapsulate these design principles for longitudinal and transverse modes respectively, and the bulk superlattice material Bi₄O₄SeCl₂ combines these effects by ordering both interface types within its unit cell to reach an extremely low thermal conductivity of 0.1 W K⁻¹ m⁻¹ at room temperature along its stacking direction. This value comes within a factor of four of air. We demonstrated that chemical control of the spatial arrangement of distinct interfaces can synergically modify vibrational modes to minimize thermal conductivity.