CuPbBi₅S₉ thermoelectric material with an intrinsic low thermal conductivity: Synthesis and properties

CuPbBi₅S₉ compounds have been investigated as gladite for years. However, there have been no significant studies on their physical and chemical properties. This work demonstrates that upon alloying with moderate Cu, Pb, Bi, and S using an appropriate preparation method, quaternary CuPbBi₅S₉ compounds can exhibit excellent figure of merit ZT within the temperature range 298–723 K. A low average velocity, low Young's modulus and Debye temperature, and large Grüneisen parameter, determined experimentally, indicate strong lattice anharmonicity in CuPbBi₅S₉ crystals. Furthermore, density functional theory calculations (local vibration of low-frequency acoustic phonons) justify the low lattice thermal conductivity of CuPbBi₅S₉ compounds. Because of the low thermal conductivity (0.514 W m⁻¹K⁻¹) and a relatively high power factor (293 μW m⁻¹K⁻²), a maximum ZT of 0.42 was achieved at 723 K for CuPbBi₅S₉ prepared by mechanical alloying combined with solid-state melting. Thus, CuPbBi₅S₉ materials are promising candidates for use as high-performance thermoelectric materials in the intermediate-temperature range.