Thermomechanical properties of metal-organic framework HKUST-1 crystals

Thermomechanical coupling widely exists in the vitrification and some practical applications of metal-organic frameworks (MOFs). However, the thermomechanical properties of MOF crystals still remain almost entirely unexplored. Here, based on in situ compression tests at elevated temperatures, we find very different mechanical behaviours in crystalline HKUST-1, a classic MOF, at different temperatures. Above 100 °C, a hyperelastic-plastic deformation is observed, which is ascribed to the partial disintegration of the MOF structure of HKUST-1 as revealed by reactive molecular dynamics simulations. Although the HKUST-1 crystals below 100 °C exhibit conventional elastic-plastic deformation, the serration behaviour of the plastic flow that is obvious at room temperature disappears at higher temperatures due to the entropic effect. Moreover, both the Young's modulus and yield strength of the elastic-plastic HKUST-1 below 100 °C significantly decrease with increasing temperature, which is attributed to the aggravation of ligand distortions at high temperatures. The strong dependence of the mechanical behaviours on temperature observed in crystalline HKUST-1 is expected to expand our current understanding of the thermomechanical behaviours of MOF crystals.