弱拓扑绝缘体材料Bi14Rh3I9的制备与电热输运性能研究

Exploring unconventional electrical and thermal transport phenomena and developing novel high-performance thermoelectric materials are important strategies to promote the massive applications of thermoelectric conversion technique in the field of waste-heat power generation and solid-state cooling. This project, on the basis of the nontrivial surface state electronic structure of topological insulators (TIs) and the unique layered stack structure of weak TIs, and by taking the layered weak TI system Bi14Rh3I9 as an example, plans to grow Bi14Rh3I9 single crystals and thin films via vertical Bridgman method and physical vapor deposition technique, and to study the electronic band structures of the bulk and surface states and lattice dynamics features by means of synchrotron radiation techniques. By employing electronic structure and molecular dynamics calculations, combining with low- and high-temperature electrical and thermal properties measurements, to investigate the transport mechanisms lying behind the bulk and surface states electrons and to reveal the unique phonon propagation behavior in this layered weak TI. Based on that, developing ways to manipulate the electrical and thermal properties independently and to optimize the overall thermoelectric performance, with a fundamental aim towards facilitating the development of weak TIs in the field of thermoelectric materials.

探索非传统的电热输运现象和开发新型高性能热电材料是促进热电转换技术在余热发电和固态制冷领域大规模应用的重要策略。本项目基于拓扑绝缘体新奇的表面态电子结构和弱拓扑绝缘体独特的层状堆垛结构，提出以层状弱拓扑绝缘体Bi14Rh3I9为研究对象，采用垂直布里奇曼法和物理气相沉积工艺制备Bi14Rh3I9单晶和薄膜，利用同步辐射技术研究弱拓扑绝缘体的体态和表面态电子能带结构和晶格动力学特征；开展电子结构和分子动力学计算研究，结合高温和低温电热输运性能测量结果，研究弱拓扑绝缘体的体态和表面态电子的输运规律，阐明层状弱拓扑绝缘体独特的声子传输行为。在此基础上，建立弱拓扑绝缘体电热输运性能独立调控的方法并优化综合热电性能，以此推动弱拓扑绝缘体在热电材料领域的发展。

开发新型高性能热电材料是促进热电转换技术在余热发电和固态制冷领域实现更大规模应用的关键。本项目围绕弱拓扑绝缘体这一类新材料展开了其电子声子输运行为和热电性能优化研究。通过第一性原理的声子谱计算和低温热导率测量，研究了弱拓扑绝缘体Bi14Rh3I9和Bi2TeI材料的晶格动力学特征和声子散射机制，发现这两类弱拓扑绝缘体具有极低的晶格热导率（低至0.3 W m-1 K-1），这与组成材料亚晶格的普通绝缘体层引起的低频振动和强烈非简谐行为密切相关，声子散射机制为低温下以低频共振声子散射为主、室温附近以强烈的声子-声子相互作用为主；计算了弱拓扑绝缘体 Bi14Rh3I9的电子能带结构，揭示其由二维量子自旋霍尔层主导的准二维电子传输行为；探索了弱拓扑绝缘体Bi14Rh3I9和Bi2TeI材料的热电性能优化方法，揭示了不同掺杂方式包括元素替换和插层对材料载流子浓度和电热输运性能的影响规律，发现Cu插层较Pd取代可以更显著提升Bi14Rh3I9材料的热电性能，而Zn取代较Cu插层可以更显著提升Bi2TeI材料的热电性能；借助X射线光电子能谱研究了Bi14Rh3I9材料的主要构成元素和掺杂元素的化学价态，揭示了由Cu插层引起的电荷转移行为；探索了拓扑绝缘体Bi2Te3和重费米子YbAl3薄膜材料的制备工艺，揭示了制备工艺对材料电热输运性能的影响规律；借助同步辐射X射线吸收精细结构表征了一类填充方钴矿热电材料的电子结构，研究了材料的能带结构与热电性能之间的联系。本项目基于弱拓扑绝缘体的热电性能研究将为开发基于拓扑绝缘体家族的新型热电材料提供有益指导。