关键词: copper selenide, phase transition, thermoelectric properties

Abstract: With good electrical properties and an inherently complex crystal structure, Cu$_{2 - x}$Se is a potential ``phonon glass electron crystal'' thermoelectric material that has previously not attracted much interest. In  this study, Cu$_{2 - x}$Se ($0 \le x \le 0.25$) compounds were synthesized by a melting-quenching method, and then sintered by spark plasma sintering to obtain bulk material. The effect of Cu content on the phase transition  and thermoelectric properties of Cu$_{2 - x}$Se were investigated in the temperature range of 300~K--750~K. The results of X-ray diffraction at room temperature show that Cu$_{2 - x}$Se compounds possess a cubic structure with  a space group of $Fm3m$ (#225) when $0.15 < x \le  0.25$, whereas they adopt a composite of monoclinic and cubic phases when $0 \le x \le 0.15$. The thermoelectric property measurements show that with increasing Cu content,  the electrical conductivity decreases, the Seebeck coefficient increases and the thermal conductivity decreases. Due to the relatively good power factor and low thermal conductivity, the nearly stoichiometric Cu$_{2}$Se compound achieves the highest $ZT$ of 0.38 at 750 K. It is expected that the thermoelectric performance can be further optimized by doping appropriate elements and/or via a nanostructuring approach.

Key words: copper selenide, phase transition, thermoelectric properties