利用离子结构调控策略探索合成A/Cu(Ag)/Te化合物及其热电性能研究

Thermoelectric material is environment friendly functional material that can convert directly heat to electricity, and vice versa. However, current materials surfer low efficiencies, which limits their broader applications. Although a few materials with thermoelectric figure of merit higher than 1.5 have been found recently, most of them are still facing practicability problem. Thus, the discovery of high performance thermoelectric materials is one of the hottest yet most difficult topics in this field. Our previous work revealed that 1) A/Cu(Ag)/Te compounds have shown superior structure modification via cation; 2) Several A/Cu(Ag)/Te compounds we obtained have exhibited thermal conductivities as low as those of Cu(Ag)/Te binaries; 3) Their band gaps and electronic structures depend on the identity and stoichiometry of the cation; which infers a possibility to optimize the electrical conductivity and Seebeck coefficient and eventually the ZT values of this type of compounds. Based on these knowledge, this proposal is aimed to systematically study the A/Cu(Ag)/Te systems (A is alkali metals, alkali earth metals, or rare earth metals), under the guidance of our strategy of structure control via cation by adjusting the cation identity and stoichiometry; focusing on their exploration syntheses, thermoelectric property investments. And to calculate and analyze electronic structures, Seebeck coefficients, carrier transport properties and lattice thermal conductivity with the aid of DFT theory, Boltzmann theory, equilibrium molecular dynamics (EMD) simulations combined with Green-Kubo autocorrelation decay method. To summary the correlations of the cation modification-crystal structure change; to elucidate the crystal structure-thermoelectric property relationship. We are hoping to discover several new thermoelectric materials, and to shed useful insight on the future study on high performance thermoelectric materials.

热电材料能实现热能和电能直接转换，但现有材料转换效率不高。近年来虽有数例优值大于1.5的材料报道，但在实用性上大都还存在局限。因此发现高效热电材料新体系是该领域的热点和难点。申请人前期发现：1）A/Cu(Ag)/Te化合物具有很好的离子结构调控性；2）获得几例该类化合物均保持了二元Cu(Ag)碲化物低热导率特征；3）该类化合物能隙和电子结构随阳离子种类和计量比可调，有望借此获得高ZT值化合物。为此，本项目拟利用离子结构调控策略，通过调节阳离子种类和计量比，系统开展A/Cu(Ag)/Te化合物探索合成；对所得化合物热电性能进行研究，并采用密度泛函理论、Boltzmann理论、平衡分子动力学模拟计算分析电子结构、赛贝克系数、载流子传输性能和晶格热导率,阐明其电子和声子结构特征，总结离子调控的结构规律和构效关系。本项目有望发现若干具高ZT值新颖化合物，为热电材料的结构调控研究提供新思路。

热电材料作为一种清洁能源材料，能够同时实现热能和电能的相互转换，但热电材料较低的能量转换效率制约其在能源领域的实际应用，因此寻找并筛选新型优质热电材料具有重大的研究意义。在本基金项目资助下，我们系统开展了阳离子诱导热电材料结构变化的及相关性能研究，发现若干高性能，低热导率的新型热电材料。对于高ZT值热电材料CsAg5Te3体系的研究中，我们提出了热导率材料设计的协同撞击作用（“Concerted Rattling”）降低热导率的新机制；对于混合价态化合物Cs2Ge3M6Q14 (M = Ga, In; Q = Se, Te)研究中，基于声子谱计算分析，我们首次提出了不同价态离子振动模式会存在弱耦合性的特点，为低热导率材料结构设计提供了新思路；此外，对四元体系A/TM/M/Q（A = 填充原子; TM = 过渡金属; M = 13主族; Q = 硫属元素）研究中，我们发现该结构中过渡金属存在多种配位环境，这种结构特点可以协调降低材料热导率；对于Cu4Bi4Se9体系研究中提出了复杂结构单胞降低晶格热导率等的结构调控机制，这些都为低晶格热导率的结构设计和理解提供了重要的参考。在这些研究基础上，我们获得了若干高ZT值的热电材料新体系，如：CsAg5Te3在727K的条件下具有约1.5的ZT值；723 K，In4Se2.95(CuI)0.01得到的最大ZT值，即ZTmax = 1.34，是目前无铅多晶In4Se3基热电材料的最大ZT值等。相关工作在Acc. Chem. Res.；J. Am. Chem. Soc. ;Angew. Chem. Int. Ed.；Adv. Mater.；ACS Appl. Mater. Interfaces.；Chem. Commun等等国际具有重要影响力杂志上发表30篇论文，申请专利2项，顺利完成预期目标。