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Super-colossal uniaxial negative thermal expansion in chloranilic acid pyrazine, CA-Pyz.

Liu, Huiyu and Gutmann, Matthias J and Stokes, Harold T. and Campbell, Branton J and Evans, Ivana Radosavljevic and Evans, John S. O. (2019) 'Super-colossal uniaxial negative thermal expansion in chloranilic acid pyrazine, CA-Pyz.', Chemistry of materials., 31 (12). pp. 4514-4523.

Abstract

There has been significant recent interest in exploiting the large dimension changes that can occur in molecular materials as a function of temperature, stress or under optical illumination. Here we report the remarkable thermal expansion properties of chloranilic acid pyrazine (CA-Pyz) co-crystals. We show that the compound shows uniaxial negative thermal expansion over a wide temperature range with a linear contraction coefficient as low as (−)1500×10−6 K−1 at 250 K. The corresponding 10% contraction between 200 and 300 K is an order of magnitude larger than in the so-called colossal contraction materials. We adopt a symmetry-inspired approach to describe both the structural changes that occur (using rotational-symmetry modes) and the thermal expansion (using strain modes). This allows an extremely compact description of the phase transition and detailed understanding of its atomic origins. We show how the coupling of primary and secondary strain modes in materials showing extreme expansion and contraction can lead to unusual reversals in the temperature dependence of cell parameters.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1021/acs.chemmater.9b01135
Publisher statement:This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
Date accepted:No date available
Date deposited:31 May 2019
Date of first online publication:28 May 2019
Date first made open access:No date available

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