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

Liu, Huiyu; Gutmann, Matthias J; Stokes, Harold T.; Campbell, Branton J; Evans, Ivana Radosavljevic; Evans, John S.O.

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


Huiyu Liu

Matthias J Gutmann

Harold T. Stokes

Branton J Campbell

Ivana Radosavljevic Evans



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.


Liu, H., Gutmann, M. J., Stokes, H. T., Campbell, B. J., Evans, I. R., & Evans, J. S. (2019). Super-colossal uniaxial negative thermal expansion in chloranilic acid pyrazine, CA-Pyz. Chemistry of Materials, 31(12), 4514-4523.

Journal Article Type Article
Online Publication Date May 28, 2019
Publication Date Jun 25, 2019
Deposit Date May 31, 2019
Publicly Available Date Jun 14, 2019
Journal Chemistry of Materials
Print ISSN 0897-4756
Electronic ISSN 1520-5002
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 31
Issue 12
Pages 4514-4523


Published Journal Article (Advance online version) (4.1 Mb)

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Copyright Statement
Advance online version 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.

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