Pulse-current sintering and thermoelectric properties of gas-atomized silicon–germanium powders

Abstract

Both p- and n-type Si 0.8Ge 0.2 powders for thermoelectric materials were prepared by gas atomizing of the corresponding ingots with boron and phosphorous, respectively, and then the dense bodies were formed by pulse-current sintering (PCS) of these powders. The effect of ball milling on sinterability and thermoelectricity was discussed. The abrupt densification of Si–Ge gas-atomized powders occurred over 1500 K due to the liquefaction of very small particles themselves and around the contact points between larger particles by the local concentration of electric current in the dense body. However, the sinterability of as-prepared powders was improved with the surface energy increased mechanochemically by ball milling. Thermoelectric properties, i.e., thermal conductivity, electrical resistivity, and Seebeck coefficient of the dense bodies were further determined in a temperature range from room temperature to 1073 K, followed by the evaluation of the figure of merit. The figure of merit of the dense body from ball-milled powders was lowered by approximately 10% due to the increase of electrical resistivity compared with that from as-prepared powders. That is, ball milling was effective for sinterability but ineffective for thermoelectricity in the fabrication of p- and n-type Si 0.8Ge 0.2 dense bodies. Furthermore, p–n-joined Si 0.8Ge 0.2 thermoelectric elements were fabricated by simultaneous sintering and joining of both types of Si–Ge gas-atomized powders.