Abstract The n-type I-V-VI2 AgBiSe2 features intrinsically low κ due to the anharmonicity of chemical bonds. Experimentally-determined isothermal section guides the starting compositions for the following AgBiSe2-based alloys. Among the undoped alloys, the Ag25Bi25Se50 exhibits a highest peak of zT∼0.75, and yet the neighboring Ag20Bi27.5Se52.5, which involves a Se-rich liquid phase, has a much lower zT∼0.3 at 748 K, respectively. With the incorporation of Ge, the (GeSe)0.03(AgBiSe2)0.97 exhibits an ultralow κ∼0.3 (W/mK), owing to the formation of Bi2Se3 nano-precipitate in the size of 20–40 nm. Additionally, the moire fringes with a periodicity of 0.25 nm are observed in the Bi2Se3 nano-precipitate, implying the presence of local mass fluctuation and superlattice, which could further lead to enhancing phonon scattering and reduced κ. As a result, the ultra-low κ∼0.3 (W/mK) boosts the peak of zT up to zT∼1.05 in n-type (GeSe)0.03(AgBiSe2)0.97, which shows a 140% enhancement compared with that of the undoped AgBiSe2.

中文翻译：

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n型Ge掺杂AgBiSe 2 热电材料中的超低热导率

摘要 n 型 IV-VI2 AgBiSe2 由于化学键的非谐性而具有固有的低 κ 特性。实验确定的等温截面指导以下 AgBiSe2 基合金的起始成分。在未掺杂的合金中，Ag25Bi25Se50 的最高峰值为 zT~0.75，而相邻的 Ag20Bi27.5Se52.5（包含富硒液相）在 748 K 时的 zT~0.3 分别低得多。随着 Ge 的掺入，(GeSe)0.03(AgBiSe2)0.97 表现出超低的 κ∼0.3 (W/mK)，这是由于形成了 20-40 nm 大小的 Bi2Se3 纳米沉淀物。此外，在 Bi2Se3 纳米沉淀物中观察到周期性为 0.25 nm 的莫尔条纹，这意味着存在局部质量波动和超晶格，这可能进一步导致增强声子散射和降低 κ。因此，