Thermoelectric Chalcostibite: Solid-State Synthesis and Thermal Properties

Abstract

In this study, thermoelectric chalcostibite (CuSbS<sub>2</sub>) compounds were fabricated using mechanical alloying (MA) and hot pressing (HP), and phase identification, microstructural observation, and thermal analysis were conducted. The thermal properties were then measured and compared with those of other Cu–Sb–S ternary compounds synthesized by the same solid-state process, namely, skinnerite (Cu<sub>3</sub>SbS<sub>3</sub>), famatinite (Cu<sub>3</sub>SbS<sub>4</sub>), and tetrahedrite (Cu<sub>12</sub>Sb<sub>4</sub>S<sub>13</sub>). Both the MA powder and HP-sintered samples contained a single-phase chalcostibite with an orthorhombic structure, and relative densities of 94.6–99.7% were obtained based on HP temperature. The full width at half maximum of the X-ray diffraction peak was significantly reduced for the HP specimens compared to that of the MA powder due to stress relaxation and grain growth during HP at elevated temperatures. However, practically no changes were observed in the lattice constants based on HP temperature. Differential scanning calorimetric analysis revealed that one endothermic reaction occurred at 814–815 K for the MA powder and at 818–821 K for the HP specimen, which were interpreted as the melting points of chalcostibite. Densely sintered compacts with densities close to the theoretical density were obtained using HP at temperatures of 623 K or higher. The constituent elements of the chalcostibites were uniformly distributed. As the HP temperature increased, thermal diffusivity and conductivity increased, but they decreased significantly as the measurement temperature increased. For the chalcostibite specimen hot-pressed at 623 K, the thermal diffusivity and conductivity were (0.75–0.36) × 10<sup>-2</sup> cm<sup>2</sup> s<sup>-1</sup> and 1.47–0.72 W m<sup>-1</sup> K<sup>-1</sup> at 323–623 K, respectively. Compared with other Cu–Sb–S ternary compounds, the thermal diffusivity was higher at low temperatures but similar at high temperatures, and the thermal conductivity above 500 K was lower than 1 W m<sup>-1</sup> K<sup>-1</sup>.