Deformation mechanism of a metal-organic framework glass under indentation

Revealing the deformation mechanism of brittle materials under sharp contact loading (indentation) is important for their applications since this knowledge is crucial for identifying the origin of flaw and scratch formation on their surfaces. As a newly emerged glass family, metal–organic framework (MOF) glasses have not been studied concerning the mechanism of their indentation-induced deformation. Here, we explore this mechanism for ZIF-62 glass (a typical MOF glass system). The fractions of densification and shear flow during indentation were determined by atomic force microscopy, while the elastic deformation was measured via nanoindentation. The results show that ZIF- 62 glass deforms primarily through densification and elastic deformation under the sharp contact loading. Significant pile-ups around indents were not observed, indicating that no or limited shear flow occurs in the glass during indentation. This behavior could be attributed to three structural factors, namely, high free volume, easily densified glass structure, and limited translational mobility of structural units.