热电材料能够实现热能与电能之间的直接相互转化，不仅能够用于固态制冷，而且可以作为深空探测器的可靠能源系统，更在废热回收领域有诱人的应用前景，因此热电材料的研究得到了广大学者的关注。中温区热电材料在废热回收及温差发电中扮演了重要的角色，PbTe基热电材料仍然是最为优异的中温区热电材料之一，但Pb的毒理性越来越被人们所关注，因而开发无铅或少铅的热电材料也逐渐受到研究者们的重视。Te元素是一种金属性非常强的非金属，因此金属碲化物往往具备窄带宽、高电导等特性，而其重的原子质量和大的离子半径也意味着较低的热导率，因此本文基于此选取了部分金属碲化物作为研究对象，对其电热输运性能进行探究及调控，实现了热电性能的提升。本文首先以低毒、储量丰富的Mn金属与Te形成的化合物MnTe为研究对象，采用机械合金化结合放电等离子烧结的制备手段合成了高质量的块材。通过Na元素掺杂引入空穴对其电性能进行了调控，在873 K实现了接近1.0的ZT值。在此基础上，研究表明固溶Se元素引入合金散射，可以实现室温热导率30 %的降低，成功使热电性能突破1.0。在MnTe中复合低热导的富Ag相被证实是一种更加有效的降低晶格热导率的手段，获得了低至非晶极限的晶格热导率。Ag的部分掺杂也能改善MnTe的电学性能，使热电性能进一步提升至1.1。相比于MnTe较差的本征电输运性质，GeTe因具有高浓度的本征Ge空位而具有极高的空穴浓度及电导率。研究表明通过过量Ge单质的自掺杂效应可以有效地抑制Ge空位的形成，进而实现空穴浓度的降低及迁移率的提升，同时在650 K以上获得了超过1.4的ZT值。在此基础上，引入少量Bi元素可实现空穴浓度的进一步优化。与此同时，菱方相GeTe对称性的提高也实现了能带简并效果，导致了态密度有效质量的增加，显著改善了电输运性质。Bi掺杂所引入的点缺陷也协同降低了热导率，使ZT值升高至2.0。本文最后研究了GeTe与MnTe相结合形成的三元立方化合物GeMnTe2，通过微观结构的表征揭示了其本征低热导的来源，即多尺度结构对声子的剧烈散射。少量Pb元素掺杂不仅能够有效地降低Ge空位的比例和空穴浓度，同时可以通过“晶格软化”及散射的加剧进一步降低晶格热导率，在823 K时实现1.4的ZT值，表明这种三元化合物也是较为优异的中温区热电材料。
Thermoelectric materials can realize the direct conversion between heat and electricity, not only can be used for solid-state refrigeration, but also as a reliable energy system for deep space detectors. It also has attractive application prospects in the field of waste heat recovery. Therefore, thermoelectric materials have attracted the attention of researchers worldwide. The medium-temperature thermoelectric materials play a pivotal role in waste heat recovery and power generation. Although the family of thermoelectric materials has been greatly enriched, PbTe-based thermoelectric materials are still one of the most excellent ones. However, the toxicity of Pb has been paid more and more attention, developing thermoelectric materials with less or even no use of Pb are desirable. Te has strong metallicity, so tellurides often exhibit narrow bandgap and high electrical conductivity, and their heavy atomic mass and large ionic radius also promise low thermal conductivity. Therefore, in this study, we dedicate to investigate the electrical and thermal transport properties of some selected tellurides and improving their thermoelectric performance.Firstly, MnTe, a compound formed by low toxicity and abundant element Mn, is investigated. The high-quality bulk samples are synthesized by mechanical alloying combined with spark plasma sintering. Electrical properties were modified by introducing holes through Na doping, and a ZT value close to 1.0 was achieved at 873 K. Furtherly, it is revealed that alloying scatter could be realized by Se alloying, which can achieve a 30% reduction of thermal conductivity at room temperature. Thus, thermoelectric performance successfully exceeds 1.0. The incorporation of Ag-rich phase with low thermal conductivity into MnTe has been proved to be a more effective way to reduce the lattice thermal conductivity, which could reach the amorphous limit. The partial doping of Ag can also improve the electrical properties of MnTe and finally increase the thermoelectric performance to 1.1.Compared with the poor intrinsic electrical transport properties of MnTe, GeTe holds a high hole carrier concentration and electrical conductivity beyond optimization, due to its easy formation of intrinsic Ge vacancies. It has shown that the Ge vacancies can be effectively inhibited by adding excess Ge to realize the self-doping effect, thereby reducing the hole carrier concentration and increasing the mobility. A ZT value exceeding 1.4 is obtained at temperatures higher than 650 K. By introducing a small amount of Bi, the hole carrier concentration is further optimized. Meanwhile, the enhanced symmetry of rhombohedral GeTe also achieves the convergence of electronic band, which leads to an increased DOS effective mass and significantly improves the electrical transport properties. The point defects introduced by the Bi doping also synergistically reduce the thermal conductivity, elevating the ZT value to 2.0.Finally, the ternary cubic compound GeMnTe2 formed by the combination of GeTe and MnTe is studied. The microstructure characterization reveals the intrinsic multiscale structure, which results in the low thermal conductivity by the strong scattering of phonons. A small amount of Pb doping can not only effectively reduce the proportion of Ge vacancies and thus the hole concentration, but also can further reduce the lattice thermal conductivity through the "lattice softening" effects and the intensification of scattering. This ternary compound is also an excellent thermoelectric material in the middle temperature region with a high ZT value of 1.4.
