Effect of extrusion process on the thermoelectric properties of hot-extruded n-type Bi2Te2.85Se0.15 compounds

The n-type Bi₂Te_2.85Se_0.15 compounds were fabricated by the hot extrusion under in the temperature range of 300 to 440°C under an extrusion ratio of 20:1. The microstructure and thermoelectric properties of the compounds were studied. It was found that the compounds was highly dense. The density was increased with increasing temperature. Also, equiaxed fine grains (~1.0 μm) were formed because dynamic recrystallization occurred during the extrusion. The hot extrusion gave rise to a slightly preferred orientation of grains. The small grain size and preferred orientation of grains and the high density contributed to an improvement in the thermoelectric properties. The highest figure of merit (2.62×10^-3/K) was obtained at 440°C. In addition, the Sbl₃ dopants significantly increased the figure of merit. The values of the figure of merit for 0.05 wt% Sbl₃-doped Bi ₂Te_0.85Se_0.15 compounds hot extruded at 440°C was 3.05×10^-3/K