Crystal structure across the β to α phase transition in thermoelectric Cu2–xSe

Here, 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 fir...

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Bibliographic Details
Published in:IUCrJ Vol. 4; no. 4; pp. 476 - 485
Main Authors: Eikeland, Espen, Blichfeld, Anders B., Borup, Kasper A., Zhao, Kunpeng, Overgaard, Jacob, Shi, Xun, Chen, Lidong, Iversen, Bo B.
Format: Journal Article
Language:English
Published: United States International Union of Crystallography 01.07.2017
Subjects:
inorganic materials
INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
negative thermal expansion
properties of solids
Research Papers
thermoelectrics
ISSN:2052-2525, 2052-2525
Online Access:Get full text
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Summary:Here, 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 peculiar zT enhancing 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 extraordinary zT enhancement across the phase transition.
Bibliography:NREL/JA-5J00-68972
USDOE
AC36-08GO28308
Danish National Research Foundation
ISSN:2052-2525
2052-2525
DOI:10.1107/S2052252517005553