新型室温热电材料的单晶生长和热电输运性能的研究

热电技术能够将电能与热能相互转化，是解决能源危机和环境问题的一种重要方案。在新型热电材料中，Mg₃(Bi,Sb)₂由于优秀的室温热电性能备受关注；SnSe具有极低的晶格热导率，进行Pb合金化后在室温下具有优秀的功率因子和热电优值zT，两者均有望成为当前最先进室温热电材料Bi₂Te₃的替代者。

通过改进布里奇曼法的坩埚设计和生长工艺，以Mg作为助熔剂便捷地制备了n-Mg₃(Bi,Sb)₂晶体。所得到的晶体表现出极高的电导率跟低的Seebeck系数绝对值。进一步的结构分析中，我们发现晶体中存在助熔剂富集的第二相，n-Mg₃(Bi,Sb)₂由助熔剂镁的富集区和镁缺失的Mg₃(Bi,Sb)₂晶格构成，半定量的元素分析显示在镁缺失的晶格中Mg与(Bi+Sb)的摩尔比接近1。

通过布里奇曼法生长了Pb掺杂的SnSe晶体，研究了Na掺杂含量对Pb-SnSe晶体的影响。结果表明Na掺杂能显著的提高Pb-SnSe的电导率和功率因子，将载流子浓度提升~10¹⁹ cm^-3。但是由于迁移率的快速下降，Na掺杂含量的继续提高对Pb-SnSe电输运性能影响不大，最佳的Na掺杂浓度位于2%左右。

在稍微过量的Se环境下生长的SnSe晶体具有更高的电导率和功率因子，这得益于载流子浓度的提高。此外由于出现了SnSe₂第二相，在过量Se环境下生长的SnSe晶体中的晶格热导率发生了下降。最终得到的Sn_0.89Na_0.02Pb_0.09Se_1.05晶体在773 K时沿b方向的热电优值zT由标准化学计量比环境下的1.51增加到了1.98。

沿着SnSe晶体的（100）解理面通过机械剥离制备了p-SnSe单晶薄膜，发现其具有良好的柔性和比较均匀的厚度（~15 μm）。热电性能测量结果表明SnSe薄膜具有近似于块体的电输运性能和良好的稳定性。将p-SnSe薄膜与n-Bi₂Te₃薄膜组合制备成π型器件，测得在ΔT=48 K时该器件功率密度达到24.04 Wm^-2，表明SnSe在薄膜热电器件领域同样具有可观的应用前景。

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