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The role of excess Sn in Cu4Sn7S16 for modification of the band structure and a reduction in lattice thermal conductivity

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Abstract

In this work, we have investigated the band structures of ternary Cu4Sn7+xS16 (x = 0–1.0) compounds with an excess of Sn, and examined their thermoelectric (TE) properties. First principles calculations reveal that the excess Sn, which exists as Sn2+ and is preferentially located at the intrinsic Cu vacancies, unpins the Fermi level (Fr) and allows Fr to enter the conduction band (CB) at x = 0.5. Accordingly, the Hall carrier concentration (nH) is enhanced by about two orders of magnitude when the x value increases from x = 0 to x = 0.5. Meanwhile, the lattice thermal conductivity (κL) is reduced significantly to 0.39 W K−1 m−1 at 893 K, which is in reasonably good agreement with the estimation using the Callaway model. As a consequence, the dimensionless TE figure of merit (ZT) of the compound Cu4Sn7+xS16 with x = 0.5 reaches 0.41 at 863 K. This value is double that of the stoichiometric Cu4Sn7S16, proving that excess Sn in Cu4Sn7S16 is beneficial for improving the TE performance.

Graphical abstract: The role of excess Sn in Cu4Sn7S16 for modification of the band structure and a reduction in lattice thermal conductivity

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Publication details

The article was received on 25 Jan 2017, accepted on 31 Mar 2017 and first published on 31 Mar 2017


Article type: Paper
DOI: 10.1039/C7TC00420F
Citation: J. Mater. Chem. C, 2017, Advance Article
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    The role of excess Sn in Cu4Sn7S16 for modification of the band structure and a reduction in lattice thermal conductivity

    T. He, N. Lin, Z. Du, Y. Chao and J. Cui, J. Mater. Chem. C, 2017, Advance Article , DOI: 10.1039/C7TC00420F

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