Directional growth and thermoelectric properties of the directionally solidified Bi ₂Te ₃-Sb ₂Te ₃ ternary alloys

The bulk thermoelectric materials of Bi ₂Te ₃-Sb ₂Te ₃ ternary alloy were prepared using a vertical Bridgman method at solidification rates ranging from 5 μm/s to 1000 μm/s. The directionally solidified microstructures with the composition of 25% Bi ₂Te ₃-75% Sb ₂Te ₃ alloy were investigated and the corresponding thermoelectric properties were measured. The results shows that the directionally solidified microstructures of 25% Bi ₂Te ₃-75% Sb ₂Te ₃ alloy only consist of Bi _0.5Sb _1.5Te ₃ single phase. At a low solidification rate of 5 μm/s, the cellular structures appear due to the solid/liquid interface losing its stabilization, and the increase of the solidification rate results in decreasing cellular structures. Additionally, the values of Seebeck coefficient and the resistivity of directionally solidified 25% Bi ₂Te ₃-75% Sb ₂Te ₃ alloys tend to a increase with increasing of the solidification rate. Under the solidification rate of 50 μm/s, the Power Factor (PF) of the alloy maintains (4.6-5.01)× 10 ^-3 W/(K ² · m) in the temperature range of 300-450 K, and its maximum value reaches 5.01 × 10 ^-3 W/(K ² · m) at 350 K. Besides, at a higher solidification rate of 500 μm/s, the maximal PF value can be measured to be 4.5 × 10 ^-3 W/(K ² · m). It seems that the Bridgman method employing high temperature gradient with rapid solidification rate is a promising approach for the preparation of thermoelectric materials with high performance. Copyright