硅基I型笼形晶体中的钡钾共填充对于载流子浓度和声子输运的影响

Type I clathrate compounds, characterized by the open frame crystal structure, demonstrate phonon-glass, electron-crystal concept well and have been intensively studied by researchers as good candidates for high temperature thermoelectric applications. Silicon based type I clathrates are friendly to the environment, whereas their moderate thermoelectric performances need further improvement. The proposed project will focus on the synthesis challenge, crystal structure and thermoelectric performances of silicon based type I clathrates as follows. 1) We will develop the synthesis methods to obtain silicon based clathrate single crystals with barium, potassium mix-occupied guest atoms, and investigate the methods to finely tune the single crystal stoichiometry.2) We will examine the influence of Ba/K mixed occupation on the carrier concentrations and determine the optimal stoichiometry of the proposed quaternary phase. 3) After carefully analyzing the samples’crystal structure and lattice thermal conductivity, we will demonstrate the phonon transport mechanism with the help of first principle calculations. The proposed work by us will present methods to control charge carrier concentration and phonon transport in crystalline materials and eventually enhance the thermoelectric performance of silicon based materials.

I型笼形物因其开放式笼框架结构而具有声子玻璃-电子晶体的特性，作为一类高温段热电材料被学术界广泛研究。目前环保型的硅基I型笼形物材料在热电性能方面还有待进一步提高，为此本课题将围绕硅基I型笼形物的材料合成、晶体结构以及热电性能等问题展开，拟重点开展以下工作：1）探索钡钾双原子填充的硅基I型笼形物的单晶生长路线以及组分调控方法；2）验证钡钾异种价电荷元素共填充可以更有效调控体系载流子浓度的可行性；确认具有最优载流子浓度和热电系数的钡钾比例；3）通过对体系晶体结构、晶格热导率的表征、分析以及第一性原理的理论计算，揭示笼形物中晶体结构-晶格热导率的构性关系和体系的声子输运机制，为有效调控载流子浓度和声子输运两方面物理性能并最终提升材料热电性能提供途径。

硅基I型笼形物具有主要由IVA族元素组成的刚性骨架，可掺杂相当量的IIIA及VA族元素实现体系的载流子调控。笼式结构内，一般占据离子化的元素，比如碱金属和碱土金属，以及一些过渡金属元素，这些位点的原子可以散射声子，具有声子玻璃-电子晶体的特性，作为一类高温段热电材料被学术界广泛研究。然而硅基I型笼形物作为热电材料还不能广泛应用，主要原因在于热电转换性能不是很理想。本项目充分考虑了材料体系特征，通过对于新型笼形化合物的挖掘和优化，实现了化学合成对于声子输运和载流子浓度的调控，提升了体系热电转换效率。本项目主要实现了：1）研究了钡钾双原子填充的硅基I型笼形物的单晶生长路线以及组分调控方法，获得了一些I型笼式化合物的新相；2）证实了钡钾异种价电荷元素共填充可以更有效调控体系载流子浓度；确认具有最优载流子浓度和热电系数的钡钾比例；3）通过对体系晶体结构、晶格热导率的表征、分析以及第一性原理的理论计算，揭示笼形物中晶体结构-晶格热导率的构性关系和体系的声子输运机制，为有效调控载流子浓度和声子输运两方面物理性能并最终提升材料热电性能提供途径。