Crystal structure across the β to α phase transition in thermoelectric Cu2−xSe
Open Access
- 13 June 2017
- journal article
- Published by International Union of Crystallography (IUCr) in IUCrJ
- Vol. 4 (4), 476-485
- https://doi.org/10.1107/s2052252517005553
Abstract
The crystal structure uniquely imparts the specific properties of a material, and thus provides the starting point for any quantitative understanding of thermoelectric properties. Cu2−xSe is an intensely studied high performing, non-toxic and cheap thermoelectric material, and here for the first time, the average structure of β-Cu2−xSe is reported based on analysis of multi-temperature single-crystal X-ray diffraction data. It consists of Se–Cu layers with additional copper between every alternate layer. The structural changes during the peculiarzTenhancing phase transition mainly consist of changes in the inter-layer distance coupled with subtle Cu migration. Just prior to the transition the structure exhibits strong negative thermal expansion due to the reordering of Cu atoms, when approached from low temperatures. The phase transition is fully reversible and group–subgroup symmetry relations are derived that relate the low-temperature β-phase to the high-temperature α-phase. Weak superstructure reflections are observed and a possible Cu ordering is proposed. The structural rearrangement may have a significant impact on the band structure and the Cu rearrangement may also be linked to an entropy increase. Both factors potentially contribute to the extraordinaryzTenhancement across the phase transition.Keywords
This publication has 54 references indexed in Scilit:
- Structure-transformation-induced abnormal thermoelectric properties in semiconductor copper selenideMaterials Letters, 2013
- Thermoelectric properties of copper selenide with ordered selenium layer and disordered copper layerNano Energy, 2012
- Copper ion liquid-like thermoelectricsNature Materials, 2012
- Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transferNature Communications, 2011
- OLEX2: a complete structure solution, refinement and analysis programJournal of Applied Crystallography, 2009
- Cooling, Heating, Generating Power, and Recovering Waste Heat with Thermoelectric SystemsScience, 2008
- Disordered zinc in Zn4Sb3 with phonon-glass and electron-crystal thermoelectric propertiesNature Materials, 2004
- Vacancy-Ordered Superstructures in Cu2Sephysica status solidi (a), 1991
- Dilatometric study of nonstoichiometric copper selenide Cu2−xSeSolid State Ionics, 1984
- dc ionic conductivity measurements on the mixed conductor Cu2−xSeSolid State Ionics, 1984