Structural Incommensurability Drives Ultralow Lattice Thermal Conductivity in Misfit Layered (BiSe)1.23CrSe2

Abstract

Owing to their remarkable structural diversity, metal chalcogenides offer an excellent platform for uncovering fundamental structure-property relationships and emergent electronic and thermal transport behaviours. Here, we report an ultralow lattice thermal conductivity in misfitlayered chalcogenide (BiSe)1.23CrSe2, composed of an alternative stacking of BiSe and CrSe2 layers along the crystallographic c-direction and incommensurability along the b-axis. The spark plasma sintered (SPS) sample exhibits an ultralow lattice thermal conductivity (κL) of ~0.52 W m -1 K -1 (SPS∥) at 296 K. Low-temperature specific heat capacity analysis of the material reveals the presence of low-frequency optical phonon modes, which arise from anharmonicity as evident from the high Grüneisen parameter (γ). The Raman spectroscopy further corroborates that these optical phonon modes have extremely short phonon lifetimes (< 1 ps). The synergistic effect of stacking disorder, layered interfaces, cation vacancies, and a high degree of anharmonicity in the bonding contributes to such a low κL. Aliovalent doping of Pb further scatters the heat-carrying phonons, leading to a minimum κL of ~ 0.31 W m -1 K -1 in SPS ⊥ over 372-423 K, which is the lowest among the reported misfit layered compounds to the best of our knowledge, and competitive among the ultralow κL materials.