Effect of Zn-Doping on the Phase Transition Behavior and Thermoelectric Transport Properties of Cu2Se

Abstract

We report on the phase transition behavior and thermoelectric transport properties of Zn-doped Cu2Se. Cu2Se is comprised of nontoxic, low-cost and abundant elements, and has been attracting attention because of its very high thermoelectric performance, ZT, at high temperatures. Many studies have reported enhanced ZT in impurity doped Cu2Se, however, little is known about the effect of dopants on the phase transition behavior of Cu2Se. In this study, we prepared (Cu1-xZn)2Se (x = 0 ~ 0.03) compounds by spark plasma sintering, and investigated the phase transition behavior in terms of the temperature-dependent thermoelectric transport properties. Undoped Cu2Se consists of monoclinic α-Cu2Se and berzelianite at room temperature. However, the crystal structure of (Cu1-xZnx)2Se compounds is changed into a single phase of α-Cu2Se with increasing Zn content. As the Zn content increased, electrical conductivity decreased and Seebeck coefficient increased due to the donor role of Zn. The phase transition temperatures of the compounds were characterized as a function of Zn content, based on the temperature-dependent electrical conductivities and Seebeck coefficients. The phase transition temperature was increased by increasing Zn content, and it was attributed to the disappearance of the berzelianite phase whose phase transition temperature is lower than that of α-Cu2Se. Detailed effects of Zn-doping on both the phase transition behavior and thermoelectric transport properties were discussed.