Intrinsically Low Thermal Conductivity in a Novel Cu-S Modified ZrS₂ Compound with Asymmetric Bonding

Materials with low thermal conductivity have received significant attention across various research fields, including thermal insulation materials, thermal barrier coatings, and thermoelectric materials. Exploring novel materials with intrinsically low thermal conductivity and investigating their phonon transport properties, chemical bonding, and atomic coordination are crucial. In this study, a novel ternary sulfide is successfully discovered, Cu₂ ZrS₃ , which is achieved by introducing copper ions into both the interlayer and intralayer of ZrS₂ . The resulting structure encompasses various coordination forms within each layer, such as [CuS₄ ], [ZrS₆ ], and [CuS₃ ], leading to pronounced phonon anharmonicity induced by the asymmetric bonding of tri-coordinated Cu atoms within the [ZrS₆ ] layer. As a result, Cu₂ ZrS₃ exhibits intrinsically low lattice thermal conductivity (κ_L ) of about 0.83 W m^-1 K^-1 at 300 K and 0.35 W m^-1 K^-1 at 683 K, which are in the exceptionally low level among sulfides. In comparison to the conventional approach of inserting guests between layers, the substitution of atoms within layers provides a novel and effective strategy for designing low κ_L materials in transition metal dichalcogenides (TMDCs).