Properties and microstructures of Bi2Te3 based compound via particulate processing route

The significance of oxygen content and grain size in sintered Bi ₂Te₃ compounds with respect to thermoelectric properties was demonstrated. Bi, Te and Se powders were mixed to a typical composition of the n-type Bi-Te base system. The powder mixtures were ball-milled in acetone and consolidated by hot pressing at 500°C. The sintered materials exhibited uniform distributions of grain size with equiaxed grain morphology. Milling time of the blended powders strongly reflected the grain size of the sintered materials. The sample produced from the powders ball-milled for 2 hours consisted of grains about 3~5 microns, while finer grain sizes (about 1 micron) were achieved by increasing ball-milling time. The oxygen content of the ball-milled powders increased with increasing milling time, and the sintering process in an Ar gas atmosphere resulted in removing oxygen by about 0.5 mass % from the powders. A relatively high Z value (about 3×10^-3/K), equivalent to that of the directionally solidified materials, was obtained. The thermoelectric properties of the sintered Bi₂Te₃ compounds were discussed in relation with the oxygen content, grain size, carrier concentration and carrier mobility