定向生长Bi_2Te_3-Sb_2Te_3三元合金热电材料的组织与性能

Directional Growth and Thermoelectric Properties of the Directionally Solidified Bi_2Te_3-Sb_2Te_3 Ternary Alloys

利用Bridgman定向凝固法,在大凝固速率范围内5～1000μm/s制备出Bi2Te3-Sb2Te3三元合金块体热电材料,并对其凝固组织和不同凝固速率下合金的热电性能进行研究。结果表明:高温度梯度和大凝固速率范围内制备的25%Bi2Te3-75%Sb2Te3合金定向凝固组织由Bi0.5Sb1.5Te3单相组织组成;在较低凝固速率5μm/s下,熔体生长平界面失稳形成胞状组织,而随定向凝固速率的增加,胞状组织减少,组织细化。不同定向凝固速率下25%Bi2Te3-75%Sb2Te3合金的Seebeck系数和电阻率随着凝固速率的增加而增大。50μm/s下300～450K范围内获得功率因子(PF)在4.6×10-3～5.01×10-3W/(K2.m),并在350K时PF值达到最大值5.01×10-3W/(K2.m);而在高凝固速率500μm/s下,其功率因子也可达4.5×10-3W/(K2.m),表明高温度梯度和大凝固速率制备热电材料是一种有效的制备工艺方法。

The bulk thermoelectric materials of Bi2Te3-Sb2Te3 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% Bi2Te3-75% Sb2Te3 alloy were investigated and the corresponding thermoelectric properties were measured.The results shows that the directionally solidified microstructures of 25% Bi2Te3-75% Sb2Te3 alloy only consist of Bi0.5Sb1.5Te3 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% Bi2Te3-75% Sb2Te3 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/(K2.m) in the temperature range of 300-450 K,and its maximum value reaches 5.01×10-3 W/(K2.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/(K2.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.