Thermal Properties of the Very Low Thermal Conductivity Ternary Chalcogenide Cu₄Bi₄M₉ (M = S, Se)

Temperature-dependent thermal properties of phase-pure polycrystalline ternary chalcogenides Cu₄Bi₄S₉ and Cu₄Bi₄Se₉ are reported. The structure and bonding in these materials result in very low thermal conductivity values (<0.8 W m⁻¹ K⁻¹ at room temperature) for both materials. The lattice contribution, Debye temperatures, and Sommerfeld coefficient are obtained from low-temperature heat capacity data that also indicate very small electronic contributions to the heat capacity for these materials. This study aids in the identification of new nontoxic, earth-abundant resistive ternary chalcogenide materials with low thermal conductivity for potential thermal barrier coating and rewriteable storage applications.