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Issue 11, 2016
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High thermoelectric performance in Te-free (Bi,Sb)2Se3via structural transition induced band convergence and chemical bond softening

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Abstract

Semiconductors with converging multiple electronic valleys and soft chemical bonds are ideal for high-performance thermoelectrics. Narrow gap Bi2Se3 is a well-known three-dimensional topological insulator with non-trivial surface states, while possessing low thermoelectric properties due to its single-degenerate band conduction, despite being an important constituent of highly efficient n-type thermoelectric Bi2(Te,Se)3. Here we demonstrate that in Te-free Bi2−xSbxSe3 converging multiple electronic band valleys and strengthening phonon scattering can be realized simultaneously via a composition-induced (Sb-alloying) structural transition from a rhombohedral phase to an orthorhombic phase. The accompanying chemical bond softening and structural distortion cause significant modifications to the electronic band structure and phonon dispersion. The convergence of heavy bands realized in the orthorhombic phase (x ≥ 1.0) largely increases the electron density of states effective mass, and thus gives rise to a high Seebeck coefficient of ∼−280 μV K−1 at 800 K. Meanwhile, phonon softening and substantial lattice anharmonicity pertain to weak interchain interactions considerably block the heat-carrying acoustic phonons, resulting in ultralow lattice thermal conductivities of ∼0.6 W m−1 K−1 at 300 K and ∼0.3 W m−1 K−1 at 800 K. Consequently, a maximum thermoelectric figure of merit ZT of ∼1.0 can be achieved for n-type BiSbSe3, about three times higher than that of the optimized Bi2Se3. The moderately high ZT of Te-free BiSbSe3 makes it a promising candidate for low-mid temperature power generations. Furthermore, the concept of structural transition driven band convergence and chemical bond softening can be applied to improve the thermoelectric properties of other materials and may also shed light on identifying new materials.

Graphical abstract: High thermoelectric performance in Te-free (Bi,Sb)2Se3via structural transition induced band convergence and chemical bond softening

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Publication details

The article was received on 13 Sep 2016, accepted on 26 Sep 2016 and first published on 26 Sep 2016


Article type: Paper
DOI: 10.1039/C6EE02674E
Citation: Energy Environ. Sci., 2016,9, 3436-3447
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    High thermoelectric performance in Te-free (Bi,Sb)2Se3via structural transition induced band convergence and chemical bond softening

    S. Wang, Y. Sun, J. Yang, B. Duan, L. Wu, W. Zhang and J. Yang, Energy Environ. Sci., 2016, 9, 3436
    DOI: 10.1039/C6EE02674E

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