Institute of Physics (IA), RWTH Aachen University, Sommerfeldstraße 14, 52074, Aachen, Germany.
State Key Laboratory of Solidification Processing, and Key Laboratory of Radiation Detection Materials and Devices, Ministry of Industry and Information Technology, Northwestern Polytechnical University, Xi'an, 710072, P. R. China.
Adv Mater. 2023 May;35(19):e2300893. doi: 10.1002/adma.202300893. Epub 2023 Mar 27.
Doping is usually the first step to tailor thermoelectrics. It enables precise control of the charge-carrier concentration and concomitant transport properties. Doping should also turn GeSe, which features an intrinsically a low carrier concentration, into a competitive thermoelectric. Yet, elemental doping fails to improve the carrier concentration. In contrast, alloying with Ag-V-VI compounds causes a remarkable enhancement of thermoelectric performance. This advance is closely related to a transition in the bonding mechanism, as evidenced by sudden changes in the optical dielectric constant ε , the Born effective charge, the maximum of the optical absorption ε (ω), and the bond-breaking behavior. These property changes are indicative of the formation of metavalent bonding (MVB), leading to an octahedral-like atomic arrangement. MVB is accompanied by a thermoelectric-favorable band structure featuring anisotropic bands with small effective masses and a large degeneracy. A quantum-mechanical map, which distinguishes different types of chemical bonding, reveals that orthorhombic GeSe employs covalent bonding, while rhombohedral and cubic GeSe utilize MVB. The transition from covalent to MVB goes along with a pronounced improvement in thermoelectric performance. The failure or success of different dopants can be explained by this concept, which redefines doping rules and provides a "treasure map" to tailor p-bonded chalcogenides.
掺杂通常是定制热电材料的第一步。它能够精确控制电荷载流子浓度和伴随的输运性质。掺杂还应该使本征载流子浓度低的 GeSe 成为一种有竞争力的热电材料。然而，元素掺杂并不能提高载流子浓度。相比之下，与 Ag-V-VI 化合物形成合金会显著提高热电性能。这一进展与键合机制的转变密切相关，这可以从光学介电常数 ε 、玻恩有效电荷、光学吸收 ε (ω) 的最大值和键断裂行为的突然变化中得到证明。这些性质变化表明形成了高价键合（MVB），导致八面体状的原子排列。MVB 伴随着有利于热电的能带结构，具有各向异性的能带和小的有效质量和大的简并度。区分不同类型化学键的量子力学图谱表明，正交 GeSe 采用共价键，而三方和立方 GeSe 则采用 MVB。从共价键到 MVB 的转变伴随着热电性能的显著提高。不同掺杂剂的成败可以用这个概念来解释，它重新定义了掺杂规则，并提供了一张“藏宝图”来定制 p 键合的硫属化物。
