Supercolossal Uniaxial Negative Thermal Expansion in Chloranilic Acid Pyrazine, CA-Pyz

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 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 responsible for this unusual behavior and gives 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.

A survey of thermal expansion coefficients for organic molecular crystals in the Cambridge Structural Database

“…In the sorted list, three structures stand out as having extreme positive and negative coefficients (Table 2). {AHEJAZ} (Das et al, 2010) has been noted above, while {BOQHOE01} has been reported recently to show supercolossal uniaxial NTE (Liu et al, 2019). Hence, the data set again appears to reflect expectations from the literature.…”

“…Structure-property relationships in crystalline materials are of fundamental importance for a huge range of research and practical applications, and the control and design of such properties is at the heart of crystal engineering. For molecular materials, thermal expansion has received some attention in the literature, for example where structures show unusually large or exceptionally anisotropic expansion (Das et al, 2010;Takahashi & Tamura, 2015;Alimi et al, 2018;van der Lee et al, 2018;Liu et al, 2019). There have also been some efforts in the crystal engineering literature to link thermal expansion to intermolecular interactions and specific structural features Bhattacharya & Saha, 2014;Saraswatula et al, 2015;Hutchins et al, 2016;Rather & Saha, 2018;Hutchins et al, 2018a;Negi et al, 2018).…”

Exploring the nature of the fergusonite–scheelite phase transition and ionic conductivity enhancement by Mo6+doping in LaNbO4

“…The use of distortion mode renements against diffraction data to describe symmetry-reducing phase transitions, both rst and second order, has been demonstrated in both extended and molecular systems. [47][48][49][50] Here it is used for the rst time to analyse and describe the phase transition between the fergusonite and scheelite structures.…”

Thermal expansion properties of organic crystals: a CSD study

“…32 An exceptional negative volumetric thermal expansion in 1,4-diazabicyclo[2.2.2]octane hydrochloride was reported by Szafrański (2013); 33 the highest reported negative uniaxial thermal expansion was found in chloranilic acid pyrazine. 34 In this paper we focus on thermal expansion properties of crystalline organic materials determined by diffraction techniques, using data mining of the Cambridge Structural Database (CSD). 35 It is shown that unusual thermal expansion properties exist for a number of crystalline compounds which have not been recognized as such before.…”