Identifying and Characterising Flexible Crystals

Abstract

Mechanically flexible single crystals are emerging as a useful class of materials due to their unique combination of crystallinity and molecular-scale responses to applied mechanical stress. In this tutorial review, we suggest best practice approaches to the identification and characterisation of these fascinating materials. These approaches can be applied in crystals that show either plastic or elastic flexibility, or a combination of the two. In particular, we highlight that the molecular mechanism of flexibility that occurs when a crystal is subject to mechanical stress varies from system to system, and so it is impossible to infer the nature of movement that will occur merely from crystal packing analysis. Understanding the structural changes that occur when a crystal is subject to mechanical stress is essential for developing their utility in a wide range of applications, particularly in optoelectronics, waveguides and piezoelectrics.