GeTe alloy is a promising medium-temperature thermoelectric material but with highly intrinsic hole carrier concentration by thermodynamics, making this system to be intrinsically off-stoichiometric with Ge vacancies and Ge precipitations. Generally, an intentional increase of formation energy of Ge vacancy by element substitution will lead to an effective dissolution of Ge precipitates for reduction in hole concentration. Here, an opposite direction of decreasing the formation energy of Ge vacancies is demonstrated by substituting Cr at Ge site. This strategy produces more but nearly homogenously distributed Ge precipitations and Ge vacancies, which provides enhanced phonon scattering and effectively reduces the lattice thermal conductivity. Furthermore, Cr atom carries one more electron than Ge and serves as an electron donor for decreasing the hole carrier concentrations. Further optimization incorporates the effect of Bi substitution for facilitating band convergence. A maximum figure of merit (ZT) of 2.0 at 600 K with average ZT of over 1.2 is achieved in the sample of Ge0.92 Cr0.03 Bi0.05 Te, making it one of the best thermoelectric materials for medium-temperature application.

中文翻译：

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通过Cr掺杂处理Ge空位和Ge沉淀，以实现高性能GeTe热电材料。

GeTe合金是一种有前途的中温热电材料，但通过热力学具有很高的固有空穴载流子浓度，使该系统本质上具有非化学计量的Ge空位和Ge沉淀。通常，通过元素置换有意增加Ge空位的形成能将导致Ge沉淀物的有效溶解以降低空穴浓度。在此，通过在Ge位点处代替Cr，表明了降低Ge空位的形成能的相反方向。这种策略会产生更多但几乎均匀分布的Ge析出物和Ge空位，从而增强声子散射并有效降低晶格热导率。此外，Cr原子比Ge携带一个电子，并作为电子给体以降低空穴载流子浓度。进一步的优化结合了Bi取代的作用，以促进频带收敛。Ge0.92 Cr0.03 Bi0.05 Te样品在600 K下的最大品质因数（ZT）为2.0，平均ZT超过1.2，使其成为中温应用的最佳热电材料之一。