Thermoelectric properties of β-Zn4Sb3 synthesized by mechanical alloying and pulse discharge sintering

Thermoelectric power generation is a helpful method for harnessing waste thermal energy, particularly covering a middle temperature range between 500 and 800 K. A beta-Zn4Sb3 compound has become the focus of attention as a thermoelectric material applicable to thermoelectric power generation around 700 K. In this research, a method combining the mechanical alloying with the pulse discharge sintering was adopted to obtain the sintered compact of beta-Zn4Sb3. Pure zinc and antimony powders were used as the starting material for mechanical alloying. These powders were mixed in the stoichiometry ratio of 4 to 3, or more Zn-rich. The mechanical alloying was carried out by planetary ball milling under conditions of fixed revolution speed and variable milling time. The influence of the milling time on the synthesis of beta-Zn4Sb3 was investigated. The sintering was executed at two sintering temperatures and under fixed conditions of sintering time, pressing pressure, and atmosphere. The influences of the sintering temperature of pulse discharge sintering on the polycrystalline grain size and the thermoelectric properties were also studied. The following results were clarified. The phases of ZnSb and Zn are easily obtained by mechanical alloying for 50 h or longer time. These phases change to a single phase of beta-Zn4Sb3 through pulse discharge sintering under the optimum condition of Zn-rich mixing. The sintered compact of beta-Zn4Sb3 with 1.17 of nondimensional figure of merit can be obtained at 673 K with the proposed mechanical alloying with pulse discharge sintering method.