Ferroelasticity has been relatively well-studied in mechanically robust inorganic atomic solids but poorly investigated in organic crystals, which are typically inherently fragile. The absence of precise methods for the mechanical analysis of small crystals has, no doubt, impeded research on organic ferroelasticity. The first example of ferroelasticity in an organic molecular crystal of 5-chloro-2-nitroaniline is presented, with thorough characterization by macro- and microscopic methods. The observed cyclic stress-strain curve satisfies the requirements of ferroelasticity. Single-crystal X-ray structure analysis provides insight into lattice correspondence at the twining interface, which enables substantial crystal bending by a large molecular orientational shift. This deformation represents the highest maximum strain (115.9 %) among reported twinning materials, and the associated dissipated energy density of 216 kJ m-3 is relatively large, which suggests that this material is potentially useful as a mechanical damping agent.
Keywords: ferroelasticity; molecular orientation; organic single crystals; twinning deformation.
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