Ultra-low thermal conductivity and improved thermoelectric performance in disordered nanostructured copper tin sulphide (Cu2SnS3,CTS)

Copper tin sulphide (Cu2SnS3, CTS) is a promising p-type thermoelectric material. In the present work, we have investigated the cation disorder in CTS disks made by sintering powders produced via high energy reactive ball-milling. The crystalline structures, electronic and thermal properties were systematically investigated. As-milled CTS shows a disordered cubic structure (c-CTS), preserved with thermal treatment up to 500 degrees C. By increasing the thermal treatment temperature, CTS gradually evolves towards the ordered monoclinic structure (m-CTS), reaching complete order at 650 degrees C. The disordered CTS has several times higher zT than the ordered CTS. In fact, ordered CTS has high thermopower, up to 700 mu V/K, and high electrical resistivity leading to zT < 0.05 above 700K; whereas, disordered (c-CTS) has comparatively high zT-0.30 above 700K. This has been related to the lower electrical resistivity, and the ultra-low thermal conductivity (k similar to 0.26 W/m-K), resulting from the disordered structure, promoting Phonon-Glass-Electron-Crystal (PGEC) characteristics. In our best knowledge, zT similar to 0.30 above 700K is the highest in CTS samples without acting on the chemistry of the system. (C) 2020 Elsevier B.V. All rights reserved.