定向凝固Ag掺杂Mg3Sb2合金热电性能

Thermoelectric Properties of Directionally Solidified Ag-doped Mg3Sb2 Alloys

摘要:

通过定向凝固方法可以制备高质量的Mg₃Sb₂晶体,根据凝固理论计算了平界面生长临界速率,在此速率下可以有效抑制第二相Sb的析出。对不同的凝固速率下的Mg₃Sb₂晶体微观组织进行了分析,表明凝固速率为5ums^_-1时可以有效减少Mg空位的出现,并在晶体中获得过量Mg原子,有利于更好的提升热电性能。通过消除晶界和Ag元素掺杂有效提升了Mg₃Sb₂晶体的载流子迁移率和浓度,在测试温度区间(300-800K)内,最大电导率值可达309Scm^_-1,同时保持了较高的Seebeck系数值,从而获得了更好的电子传输性能(PF_max=1.2mWm^_-1K^_-2),通过Hall测试和第一性原理计算对此结果进行了验证。Ag掺杂浓度为2.5at%下相应的热电优值最高可以达到0.67,此方法为Mg₃Sb₂基热电材料性能优化提供了新的路径,也为制备高性能的Mg₃(Sb, Bi)₂三元合金提供参考。

关键词:定向凝固;晶体生长;热电材料;Mg₃Sb₂

Abstract:

High quality Mg₃Sb₂ crystals were successfully prepared by directional solidification method. The critical velocity of planar interface of single-phase Mg₃Sb₂ crystal was predicted according to the solidification theory, and the precipitated Sb phase can be inhibited below this rate. Microstructure analysis of Mg₃Sb₂ crystals at different solidification rates indicates that, the quantity of Mg vacanices can be effectively reduced. The excess Mg atoms in the crystals is conducive to the improvement of thermoelectric performance. Carrier mobility and concentration of Mg₃Sb₂ crystal is tincreased by grain boundry eliminated and Ag doping. On the premise of keeping a high Seebeck coefficient, the maximum electric conductivity is 309Scm^_-1 at the testing temperature range of 300-800K. As a result, a better electronic transport properties of PF=1.2mWm^_-1K^_-2 is obtained. This result is verified by Hall testing and first-principle calculations. Correspondingly, the maximum ZT value is 0.67 at the doping concentration of 25at%. This method developed in this pape provides a new path for the performance optimization of Mg₃Sb₂-based thermoelectric materials, and also provides a reference for the preparation of high-performance ternary Mg₃(Sb, Bi)₂ alloy.

Key words:directional solidification; crystal growth; thermoelectric materials; Mg₃Sb₂