Plastic avalanches in metal-organic framework crystals

TL;DR

This study reveals that metal-organic framework crystals, specifically HKUST-1, exhibit plastic avalanches and serrated flow during compression, driven by local phase transitions, which influence their mechanical properties and potential applications.

Contribution

It uncovers the mechanism of plastic avalanches in MOF crystals through experimental and simulation studies, expanding understanding of their plasticity and phase behavior.

Findings

Plastic avalanches observed in HKUST-1 crystals during compression.

Serrated flow linked to local phase transitions.

Loading-history affects Young's modulus in MOF crystals.

Abstract

The compressive properties of metal-organic framework (MOF) crystals are not only crucial for their densification but also key in determining their performance in many applications. We herein investigated the mechanical responses of a classic crystalline MOF, HKUST-1 by using in situ compression tests. A serrated flow accompanied by the unique strain avalanches was found in individual and contacting crystals before their final flattening or fracture with splitting cracks. The plastic flow with serrations is ascribed to the dynamic phase mixing due to the progressive and irreversible local phase transition in HKUST-1 crystals, as revealed by molecular dynamics and finite element simulations. Such pressure-induced phase coexistence in HKUST-1 crystals also induces a significant loading-history dependence of their Young's modulus. The observation of plastic avalanches in HKUST-1 crystals here not only expands our current understanding of the plasticity of MOF crystals but also unveils a novel mechanism for the avalanches and plastic flow in crystal plasticity.