碲化铋基合金的本征点缺陷调控及其热电性能优化

Decoupling of interdependent thermoelectric parameters is considered as an effective way to enhance the thermoelectric performance of bulk thermoelectric materials. Intrinsic point defects widely exist in thermoelectric materials and play relatively independent impact on the carrier and phonon transport. Herein, intrinsic point defect engineering is introduced to simultaneously optimize the electrical and thermal properties of thermoelectric materials, and the bismuth telluride based alloys, which have the typical crystal structure and important application background, are selected as the research object to demonstrate the applicability of this new approach. Through studying the type, quantity and distribution characteristics of point defects based on different matrix composition and crystal structure by advanced characterization methods, the formation mechanism of point defects will be clarified. The influence of multicomponent alloy, nominal stoichiometric ratio and doping elements on the point defects will be studied in order to develop the chemical modulation technology. The influence of preparation technology, including ball milling and hot deformation, on the donor-like effect will be studied in order to develop the mechanical modulation technology. The influence of subsequent heat treatment such as annealing on the donor-like defects will be studied in order to develop the thermal modulation technology. The proposed investigation is aimed at revealing the mechanism of action of point defects on the carrier and phonon transport, exploring the possibility of simultaneous optimization of electrical and thermal properties and thermoelectric performance breakthrough. This research has important implications for the application of intrinsic point defects engineering in other thermoelectric materials and function materials.

使互相关联的热电参数去耦合化是块体热电材料性能获得突破的有效途径。本征点缺陷广泛存在于热电材料中，且对载流子和声子输运过程的影响相对独立。因而，本项目提出本征点缺陷工程以同时优化材料的电学和热学性能，并选择具有典型晶体结构和重要应用背景的碲化铋基合金为研究对象来表明这种新策略的有效性。本项目拟通过多种先进表征手段研究不同基体成分、不同晶体结构下点缺陷的类型、数量及分布特征，阐明点缺陷的形成演变机制；研究多元化、非名义化学计量比成分设计及外来掺杂元素对点缺陷的影响，开发点缺陷的化学调控技术；研究球磨、热变形等制备工艺对类施主效应的影响，开发点缺陷的机械调控技术；研究退火等后续热处理对类施主缺陷的影响，开发点缺陷的热调控技术；揭示点缺陷对载流子和声子输运的作用机制，探索电声输运协同优化和热电性能突破的途径。本项目的研究对本征点缺陷工程在其他热电材料及功能材料中的应用具有重要意义。

本项目通过实验与理论计算相结合，阐明了Bi2Te3合金中本征点缺陷的形成机制，提出并拓展了Bi2Te3本征点缺陷的化学成分调控原理，即电负性差和原子尺寸差模型。通过等电子的第三主族In元素掺杂，首次发现当电负性差和原子尺寸差产生矛盾时，本征点缺陷及载流子浓度不再是线性变化，对Bi2Te3本征点缺陷的化学成分调控提供了新的认识。通过调控放电等离子体烧结温度和热变形温度实现了粉末冶金化过程类施主效应的有效调控，开发了Bi2Te3合金本征点缺陷的热调控技术，拓展了Bi2Te3体系载流子浓度优化的途径。通过增加热变形次数或增加变形量有效促进类施主效应，开发了碲化铋本征点缺陷的机械调控技术。结合化学成分调控、机械调控与热调控技术，首次通过强类施主效应抑制了双极扩散效应。. 在实现对碲化铋体系本征点缺陷有效调控的基础上，开发了一系列具有先进热电性能的碲化铋合金。提出深能级工程实现了对窄带隙碲化铋合金少数载流子的有效调控，通过In合金化诱导的深能级、拓宽的带隙、增加的导带有效质量及等电子置换，弱化了Seebeck系数的温度依赖性并降低了双极扩散热导率，制备了具有最高平均zTave值的p型Bi0.396Sb1.525In0.075Cu0.004Te3合金。开发了革新热变形技术，通过更大的变形量、更多的变形次数以及更低的多次变形温度，在传统的n型Bi2Te2.3Se0.7合金中实现了短程无序（多种缺陷）、长程有序（高结晶度）以及强织构（近乎完全取向）的平衡，n型Bi1.95Sb0.05Te2.3Se0.7合金的最高zT值在450 K达到了1.3，是当时报道的最高值。根据本征点缺陷调控原理，开发了面向室温制冷应用的新型n型Bi2-xSbxTe3合金，提出了调控类施主效应的抑制机制与补偿机制，n型Bi1.5Sb0.5Te3合金的最高zT值在室温附近达到了1.0，优于目前报道的大多数传统n型Bi2Te2.3Se0.7合金。以上成果有望揭示块体材料电声输运协同优化及热电优值突破的有效途径。