The effect of SPS sintering temperatures on the structure, thermoelectric properties, and scattering mechanism of Cu2Se

Cu2Se has recently received much attention due to its excellent thermal and electrical transmission characteristics. In this study, Cu2Se compounds were synthesized by vacuum melt-annealing method and sintered by discharge plasma sintering (SPS) in the 793–1093 K temperature range. The effects of SPS temperatures of 793, 893, 993, and 1093 K on the phase composition, microstructure, band structure, and thermoelectric properties of Cu2Se samples, as well as the test stability of Cu2Se at high temperatures were studied. The results show that the sintering temperature affects the thermoelectric properties, microstructure, and energy band structure of Cu2Se compounds. The samples show many component segregations with nano-micron size and irregular morphology. According to conductance ratio analysis, the primary mechanism of carrier scattering is ionized impurity scattering, consistent with the change of carrier mobility with the test temperature. Combined with the XPS analysis results and defect balance equation, the mechanism of the test temperature depends on carrier concentration, and the carrier scattering mechanism is reasonably explain. The lattice thermal conductivity of Cu2Se materials is relatively low at all sintering temperatures due to nano-micron segregation and the presence of high-mobility Cu ions. Especially at the sintering temperature of 893 K, the segregation of nano-micron components is the most uniform, and the segregation particle size is the smallest, effectively enhancing the phonon scattering and making the lattice thermal conductivity the lowest. At 873 K, the ZT of Cu2Se sintered at 893 K reaches a maximum value of 1.34.