Bonding Heterogeneity in Mixed-Anion Compounds Realizes Ultralow Lattice Thermal Conductivity

Abstract

<p><a>Crystalline materials with intrinsically low lattice thermal conductivity (</a><i>κ</i><sub>lat</sub>) pave the way towards high performance in various energy applications, including thermoelectrics. Here we demonstrate a strategy to realize ultralow <i>κ</i><sub>lat</sub> using mixed-anion compounds. Our calculations reveal that locally distorted structures in chalcohalides MnPnS<sub>2</sub>Cl (Pn = Sb, Bi) derives a bonding heterogeneity, which in turn causes a peak splitting of the phonon density of states. This splitting induces a large amount of scattering phase space. Consequently, <i>κ</i><sub>lat</sub> of MnPnS<sub>2</sub>Cl is significantly lower than that of a single-anion sulfide CuTaS<sub>3</sub> with a similar crystal structure. Experimental <i>κ</i><sub>lat</sub> of MnPnS<sub>2</sub>Cl takes an ultralow value of about 0.5 W m<sup>−1</sup> K<sup>−1</sup> at 300 K. Our findings will encourage the exploration of thermal transport in mixed-anion compounds, which remain a vast unexplored space, especially regarding unexpectedly low <i>κ</i><sub>lat</sub> in lightweight materials derived from the bonding heterogeneity.</p>