类金刚石三元硫化物热电材料新型微结构构建与性能优化

Thermoelectrics can realize the interconversion between heat and electricity power, and therefore are of great potential in energy saving and environment protection through waste heat harvest. In this proposal, diamond-like ternary sulfides are targeted for microstrure engineering and performance optimization. Based on thermoelectric priciples and theories, diamond-like ternary sulfides are selected for microstructural manipulation from atom-, nano- and nano-micro-dimension levels to synergistical control of electrical and phonon transport. The comprehensive effects of doping of the matrix and its structure on the suppresion of cation electromigration, control of crystal structure and cation occupation, in-situ nano-precipitation, and the enhancement of density-of-statesand band convergence will be studied, to realize the complementary tailoring of the structural and electrical stability and the transport properties of phonons and electrons. By the nano-composite approach, the effect of ionized scattering will be incorporated to enhance the thermopower; a special structure using few-layered 2D sulfides laminated between the grain boundaries of matrix is proposed to make use of the effects of electron-transmitting and phonon-blocking , high density-of-state due to low-dimensionality, and energy filtration, in order to further enhance the performance of the matrix. The research will make a deep insight into the structure-performance relationship, promoting a potential application of the diamond-like ternary sulfides as an environmentally friendly thermoelectric with theoretical and technological supports.

热电材料能实现热能和电能相互转换，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类金刚石三元硫化物热电材料的微结构调控与性能优化。根据热电材料理论和硫化物物理化学特性选择类金刚石结构三元硫化物，并从原子层级、纳米、纳微层级多方位设计微结构，实现对电、声输运的优化协同调控；研究掺杂对基体材料Cu迁移抑制、晶型与阳离子分布控制、原位纳米析出诱发以及态密度和能带收敛影响的作用规律，优化组成与微结构以提高结构与电学稳定性以及电子、声子输运特性的协同调控作用。通过纳米复合方法，引入离化散射机制提升功率因子；构建少层二维硫化物夹层结构晶界，利用其“电子透过-声子阻挡”、低维化态密度高的特性和能量过滤效应，全方位提高类金刚石结构硫化物的热电性能。本研究将为深入理解该类硫化物的构效关系、挖掘热电性能潜力，促进其作为环境友好型热电材料的开发与应用提供理论和技术支撑。

类金刚石三元硫化物是环境友好型热电材料的重要分支，本课题围绕探究了Cu2SnS3（CTS）基材料的微观结构、能带结构及声子-电子输运关系，实现了CTS基热电性能的有效提升；创新发展了液相辅助高速剪切工艺，实现了多个层状体系热电性能的重要突破。主要研究内容和成果包括：.1. 形成了Cu基金刚石结构Cu2SnS3(CTS)热电材料新体系.(1) 立方相和四方相CTS的高对称性和能带简并度及金属阳离子无序性，有利于提高态密度有效质量和抑制晶格热导率kL；掺杂具有d空轨道的元素可促进态密度和有效质量的提高，磁性元素顺磁-铁磁转变对载流子浓度产生一定影响，而热电性能基本上受d轨道电子状态支配；.(2) 晶界复合MoS2、凹凸棒土等纳米相形成了载流子能量过滤及施主掺杂效果，Sb施主掺杂在提高态密度同时产生载流子弥合作用，富Sn组成抑制了受主(Co)掺杂的效果，这些方法在维持功率因子（PF）基本不变甚至提升的同时，有效降低了载流子浓度和电导率以及电子热导率，同时借助界面声子散射和合金效应进一步减小晶格热导率，最终，以20%Co掺杂CTS为基础，凹凸棒土复合后ZT最大值达到0.96，优化Sb掺杂后ZT最大值达到0.88，而富Sn5%时获得ZT~1.03的纪录值。.2. 开创了“液相辅助高速剪切-放电等离子烧结”多晶织构陶瓷新工艺，研究了晶体缺陷形成作用，实现了多个层状热电材料体系的性能优化。通过该工艺，获得了粒度细化、径厚比增大、高结晶度的粉体，烧结块体织构度显著提升，实现载流子迁移率、晶格热导率的协同调控，为超细粉体加工、高织构化层状结构多晶纳-微米陶瓷的制备及其在热电等多领域的应用开辟了新技术路线。TiS2织构块体ZT值达到了0.7，近乎现纪录值的2倍；BiCuSeO、Bi2O2Se等的ZT值也接近或成为目前最高记录。