硫化物体系环境友好型热电材料的微观结构控制与热电变换特性的研究

Thermoelectric materials can realize the conversion between temperature difference and electricity power, and therefore are of great potential in energy saving through power generation by harvesting waste heat and contribution to environment protection by reducing green-house gas emission as well.In this project, metal-sulfide-based nano-composites are targeted, which are to be formed either by compaction of nanoscale constituents (nanoparticles, nanowires, etc.) into bulk samples or by in situ precipitation of nanoscale constituents by means of phase separartion, so that the lattice thermal conductivity could be suppressed by substantially enhanced phonon-interface scattering, and the power factor could be improved by syneretic virtue of energy filtering that low energy carriers are selectively scattered, in addiation to electrical transport optimization by carrier concentration adjustment through suitable doping, and the primary goal is ZT≥0.8(N- and P-type). Thermoelectric modules will be fabricated using the prepared bulk samples and tested in air to examine the conversion efficiency and the durability in order to find and solve possilble technological problems toward practical application..Moreover,through the systematic work, the effects of composition and synthetic process on the microstructural features will be investigated to establish an effective and reasonable synthetic route of nano-composites with controllability over the crystallography of the composite, grain size and its distribution of the nano-inclusions. More importantly, the dependence of thermoelectric properties on the microstructural features including the grain boundaries will be clarified from the physical mechanism piont of view so as to manipulate the composition and synthetic process to optimize the thermoelectric performance..Thus, both theoretically and technologically, fundamental knowledges on utilization of metal-sulfide-based materials as thermoelectris are furthered, providing a solid platform for further improvement of their performance and applicability.

热电材料能实现热能和电能相互转换，它的应用对于废热利用、促进节能环保具有重要意义。本项目致力于环境友好型硫化物体系热电材料的微观结构的调控与电热输运机制的研究。根据固体物理和半导体物理原理和硫化物物理化学特性合理选择组成，并通过软化学合成和原位分相或其它方法，制备纳米化复合结构体材料；借助基体中纳米复合相(纳米颗粒、纳米线等)加强声子散射以降低热导率以及电子能量过滤以增大功率因子，通过掺杂调节载流子浓度优化电子输运特性，从而达到较高的热电转换性能(目标ZT≥0.8,N型和P型)；试制和测试热电模块，发现和解决实用化过程中的技术问题。本研究通过考察并分析物相和化学组成、合成和制备工艺对微观结构的内在联系，建立合理有效的控制微观结构的实验路线；分析物相和化学组成、微观结构与电子输运特性以及热电变换性能之间的相互作用，增进对硫化物热电材料的理解，为实现硫化物热电材料性能实用化提供理论和技术支撑。

本项目围绕高性能环境友好型硫化物, 着重研究了N型硫化钛基块体和薄膜材料、以及P型Cu-Sn-S基块体材料的组成、合成与制备工艺、微结构及其对热电性能的影响与作用机理. 研究结果表明:. (1) 对于N型TiS2基材料, 高能机械球磨法制备的纳米复合材料可控制载流子浓度增大, 在获得接近于插层物的晶格热导抑制效果的同时降低电子热导率进而获得较低的总热导率, 并可引入能量过滤(如TiS2-xPbS, TiS2-xMoS2及TiS2-xPbSnS3纳米复合块体)、离化杂质散射效应(如TiS2-xAgSnSe2纳米复合块体)以优化功率因子, 其中, 引入AgSnSe2为复合相时, 高温功率因子可达1.3~1.5 mW/(m K2), ZT 在773K时达到最大值0.85, 几乎是TiS2体系文献报道最高值的2倍; 以TiS2为基体, 由有机物插层-剥离-沉降法制备的柔性热电膜具有较高的机械和电学柔性, 试验组装的柔性器件达到了较高的输出功率, 显示了该材料与方法在柔性热电材料研发中的良好前景; . (2) 对于P型Cu基硫化物材料, 发现 Cu2(Sn, M)S3 (M = 掺杂元素Zn、Ni、Co等)具有极佳的声子玻璃-电子晶体特性. 掺杂后呈金属原子无序占位的高对称相, 且微结构中存在原位析出的大量数十~数百纳米的富Cu纳米相, 尤其是, 基体相具有明显的数纳米尺度的金属原子有序/无序纳米马赛克结构, 这些结构特征大大加强了声子散射, 以致高温晶格热导率接近于理论最低值0.3 W/(m K); 另外, 高比例受主掺杂赋予该体系优秀的电输运性质, 其电导率与赛贝克系数可实现大幅调制, 最高功率因子可达0.8~1.1 mW/(m K^2), ZT可达0.6~0.82 (723 K), 可媲美于性能最好的传统热电材料的同温值; 然而纳米复合研究表明, 功率因子和热导率的协同优化作用有限. . 通过本项目研究, 实现硫化物较高的ZT, 均达到硫化物体系的当前最优水平, 对硫化物环境友好型热电材料的高性能化及实用化推进提供了重要实验和理论参考依据.