Ultralow thermal conductivity in n-type Ge-doped AgBiSe2 thermoelectric materials

• Published in: Acta materialia Vol. 141; pp. 217 - 229
• Main Authors: Wu, Hsin-Jay, Wei, Pai-Chun, Cheng, Hao-Yen, Deng, Jie-Ru, Chen, Yang-Yuan
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-12-2017
• Subjects: Bi2Se3 nano-precipitate; Isothermal section; n-type AgBiSe2; Thermoelectric material; Bi2Se3 nano-precipitate; Thermoelectric material; n-type AgBiSe2; Isothermal section
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2017.09.029

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 moiré 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.
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