Sinterability and Thermoelectric Properties of p- and n-Type Si-Ge Powders Prepared by Gas-Atomizing Method

Abstract

Both p- and n-type Si_0.8Ge_0.2 powders (Si : Ge : B=79.7 : 20.1 : 0.20 mol% for p-type and 79.8 : 20.0 : 0.20 mol% for n-type) were prepared by gas atomization of the melts from starting solids, followed by densification using a pulse-current sintering technique. These Si-Ge powders were characterized and their sinterability was studied, and the thermoelectricity of the Si-Ge dense bodies was then elucidated. The effect of ball-milling on both the sinterability and thermoelectricity was discussed. Ball-milling made the particle size of as-prepared powders small, presumably together with the introduction of the distortion to the crystal lattice. The densification of as-prepared powders was abruptly promoted above 1500 K by pulse-current sintering, while this densification behavior of the pulverized powders occurred at a lower temperature by approximately 100 K. The grain size and elemental inhomogeneity of the dense body from pulverized powders were also reduced. The pulse-current sintering of the gas-atomized and their pulverized powders led possibly to a density of the shaped bodies of more than 99% at 1523 and 1433 K, respectively, in a short time of 3 min. The following results obtained here were all attributed to the thermoelectric properties such as thermal conductivity, electrical resistivity and the Seebeck coefficient of the dense bodies. The figure of merit of dense body from gas-atomized n-type powder was the highest among the four kinds of the dense bodies tested. It is proved that the figure of merit of the dense bodies from gas-atomized powders was higher than those from pulverized powders, and that further pulverization by ball-milling was ineffective.