Obtaining Material Based on Copper Selenide by the Methods of Powder Metallurgy

Copper selenide is a promising material for power generation in a medium-temperature range 600–1000 K. A number of features of the Cu–Se system, namely, the existence of phase transition in a Cu2Se compound, the high speed of the diffusion of Cu ions, and the high vapor pressure of Se at elevated temperatures, make it necessary to carry out a series of experimental investigations to develop and optimize the methodology for obtaining the bulk material based on copper selenide. The influence of mechanochemical synthesis regimes and subsequent compaction method on the thermoelectric properties and structure of copper selenide is studied. The source material is obtained by mechanochemical synthesis. The methods of hot pressing (HP) and spark plasma synthesis (SPS) are used to obtain the bulk samples. The investigation of the structure and phase composition is performed by the X-ray diffraction and scanning electron microscopy. It is shown that increasing the duration of the mechanochemical synthesis up to 5 h leads to the depletion of copper in powders and to the formation of nonstoichiometric β-phase Cu1.83Se, which persists after SPS. A comparison of the structure and properties of the material obtained by SPS and HP showed that the material obtained by HP has a greater degree of grain defects. The highest thermoelectric efficiency ZT = 1.8 at a temperature of 600°C is achieved for the material obtained by SPS. It is shown that low thermal conductivity is the main factor affecting the value of the thermoelectric efficiency ZT of the studied materials. The difference in the values of thermal conductivity of the materials obtained by different methods is related to the electronic component of thermal conductivity.