Grain boundaries (GBs) form ubiquitous microstructures in polycrystalline materials which play a significant role in tuning the thermoelectric figure of merit (ZT). However, it is still unknown which types of GB features are beneficial for thermoelectrics due to the challenge of correlating complex GB microstructures with transport properties. Here, it is demonstrated that GB complexions formed by Ga segregation in GeTe-based alloys can optimize electron and phonon transport simultaneously. The Ga-rich complexions increase the power factor by reducing the GB resistivity with slightly improved Seebeck coefficients. Simultaneously, they lower the lattice thermal conductivity by strengthening the phonon scattering. In contrast, Ga₂Te₃ precipitates at GBs act as barriers to scatter both phonons and electrons and are thus unable to improve ZT. Tailoring GBs combined with the beneficial alloying effects of Sb and Pb enables a peak ZT of ≈2.1 at 773 K and an average ZT of 1.3 within 300–723 K for Ge_0.78Ga_0.01Pb_0.1Sb_0.07Te. The corresponding thermoelectric device fabricated using 18-pair p-n legs shows a power density of 1.29 W cm⁻² at a temperature difference of 476 K. This work indicates that GB complexions can be a facile way to optimize electron and phonon transport, further advancing thermoelectric materials.

中文翻译：

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晶界络合能够同时优化电子和声子传输，从而实现高性能 GeTe 热电器件

晶界 (GB) 在多晶材料中形成无处不在的微观结构，在调节热电品质因数 ( ZT ) 方面发挥着重要作用。然而，由于将复杂的晶界微观结构与传输特性相关联的挑战，目前尚不清楚哪种类型的晶界特征有利于热电。在这里，证明了 GeTe 基合金中 Ga 偏析形成的 GB 络合物可以同时优化电子和声子传输。富含 Ga 的表面通过降低 GB 电阻率和略微改善的塞贝克系数来增加功率因数。同时，它们通过加强声子散射来降低晶格热导率。相反，Ga ₂ Te ₃GB 处的沉淀物充当散射声子和电子的屏障，因此无法改善ZT。定制 GB 与 Sb 和 Pb 的有益合金化作用相结合，使Ge _0.78 Ga _0.01 Pb _0.1 Sb _0.07 Te在 773 K 时的峰值ZT ≈2.1，在 300–723 K 内平均ZT为 1.3 。使用 18 对 pn 腿制造的相应热电装置在 476 K 的温差下显示出 1.29 W cm ^-2的功率密度。这项工作表明 GB 肤色可以成为优化电子和声子传输的简便方法，进一步推进热电材料。