Title

New Insights into the Structure, Chemistry, and Properties of Cu4SnS4

Abstract

The ambient temperature structure of Cu4SnS4 has been revisited and the recently reported low temperature structure has been confirmed from single-crystal X-ray diffraction data. A structural phase transition from a large monoclinic unit cell at low temperature to a smaller orthorhombic unit cell at high temperature has been observed. The room temperature phase exhibited disorder in the two copper sites, which is a different finding from earlier reports. The low temperature monoclinic form crystallizes in P21/c space group, which is isostructural with Cu4GeS4. The phase transition has also been studied with variable temperature powder X-ray diffraction and 119Sn Mössbauer spectroscopy. The Seebeck coefficients and electrical resistivity of polycrystalline Cu4SnS4 are reported from 16 to 400 K on hot pressed pellets. Thermal conductivity measurements at high temperatures, 350 – 750 K exhibited very low thermal conductivities in the range 0.28 – 0.35 W K-1 m-1. In all the transport measurements the phase transition has been observed at around 232 K. Resistivity decreases, while Seebeck coefficient increases after the phase transition during warming up from low to high temperatures. This change in resistivity has been correlated with the results of first-principles electronic band structure calculations using highly-accurate screened-exchange local density approximation. It was found that both the low hole effective mass of 0.63 me for the Γ→Y crystallographic direction and small band gap, 0.49 eV, are likely to contribute to the observed higher conductivity of the orthorhombic phase. Cu4SnS4 is also electrochemically active and shows reversible reaction with lithium between 1.7 and 3.5 volts.

Department(s)

Chemistry

Second Department

Physics

Third Department

Materials Science and Engineering

Keywords and Phrases

119-Sn Mossbauer; Band structure; Crystal structure; Cu4SnS4; Electronic properties; Phase transition; Thermoelectrics; Calculations; Energy gap; Local density approximation; Seebeck coefficient; Single crystals; Temperature; X ray diffraction

International Standard Serial Number (ISSN)

224596

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2017 Academic Press Inc., All rights reserved.

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