非塑性形变晶格位错提升IV-VI族热电性能的研究

To minimize the lattice thermal conductivity for improving thermoelectrics, strategies typically focus on the scattering of low-frequency phonons by 2D-interfaces and high-frequency phonons by 0D-point defects. However, phonons with mid-frequencies contribute largely to the lattice thermal conductivity and are important to be scattered for thermoelectrics. It is theoretically known that mid-frequency phonons can be effectively scattered by 1D dislocations, but the required density is usually significantly lager than that can be obtained in thermoelectrics, because the poor plasticity as compared to metals due to their covelent/ionic chemical bonds. It is therefore necessary to increse the dislocation density by a design on chemical composition in thermoelectrics. Based on our long-term research on IV-VI thermoelectrics and their broad tunability in composition, a strategy of ‘inducing the nuclearation of lattice dislocation by vacancies and promoting the multiplication by electrostatic interactions throug aliovalent impurities is proposed here. The composition dependent dislocation density, the effect of dislocation on latice thermal conductivity will be focused on, to develop the controllability of dislocation, to model the properties quantitatively and to establish a design criteria for improving thermoelectric performance of IV-VI materials by dislocations. This project potentially provides scientific basis for enhancing thermoelectric performance via dislocation engineering.

降低晶格热导率是提升热电性能的重要途径，现有研究主要通过零维点缺陷及二维面缺陷散射声子。但这些缺陷仅对高频及低频率声子传输有较强的阻碍作用，材料的晶格热导率很大一部分源自中频声子。因此，有效散射中频声子对提升热电性能意义重大。理论研究表明一维线缺陷位错能有效阻碍中频声子传输，但热电材料通常由共价或离子键构成，不具备和金属相当的塑性变形能力，所能获得的位错浓度远低于理论预测所需。通过化学组成设计提高位错浓度、降低晶格热导率是提升热电材料性能的关键。本项目基于前期IV-VI族热电材料的研究基础及该类材料宽泛的化学组成可调特性，提出通过引入空位驱动晶格位错形成、通过带电杂质掺杂与位错的静电作用促进增殖的思路，研究该类材料化学组成对位错浓度的影响规律、位错对晶格热导率的作用机制，发展位错调控技术，建立性能评价模型，获得位错调控提升热电性能的设计方案。本项目有望为位错调控提升热电性能提供研究依据。

热电转换在清洁能源和固态制冷等领域具有不可替代的地位，解决热电材料中导电但不导热的基本矛盾、提高材料的热电性能是研究重点。本项目主要以IV-VI族热电材料为研究对象，以降低晶格热导率为研究目标，通过引入了晶体周期性边界条件的影响，改进了沿用100多年的德拜晶格热导理论模型，阐明了晶内位错对强烈散射声子及降低晶格热导率的作用机制；发展了通过空位及间隙杂质缺陷的聚集、获得高密度稳定晶内位错结构的方法，大幅度降低了材料的晶格热导率；获得了高热电性能的经典IV-VI族热电材料，有望在温差发电应用领域发挥重要作用。本项目在研期间，以通讯作者身份在Joule、Adv. Mater.、J. Am. Chem. Soc.、Adv. Energy Mater.、Adv. Funct. Mater.、Adv. Sci.、Natl. Sci. Rev.等期刊发表SCI论文44篇，其中IF~10的期刊论文34篇，授权及申请专利14项，培养博士及硕士毕业生15名，培养了一批高水平人才队伍。