Observation of indentation-induced shear bands in a metal−organic framework glass

Abstract

Metal−organic framework (MOF) glasses are a newly emerged family of melt-quenched glasses. Recently, several intriguing features, such as ultrahigh glass-forming ability and low liquid fragility, have been discovered in a number of zeolitic imidazolate frameworks (ZIFs) that are a subset of MOFs. However, the fracture behavior of ZIF glasses has not been explored. Here we report an observation of both cracking pattern and shear bands induced by indentation in a representative melt-quenched ZIF glass, that is, ZIF-62 glass (ZnIm1.68bIm0.32). The shear banding in the ZIF glass is in strong contrast to the cracking behavior of other types of fully polymerized glasses, which do not exhibit any shear bands under indentation. We attribute this anomalous cracking behavior to the easy breakage of the coordinative bonds (Zn−N) in ZIF glasses, since these bonds are much weaker than the ionic and covalent bonds in network glasses.

Tensile ductility and necking in consolidated amorphous alumina

“…Using OVITO, 39 we further analyzed the atomic shear strain and defect (dangling bond) distribution in the samples at representative strains as seen in Figure 1C,D. At 12% strain, the AQ sample displays strain localization in the form of multiple shear bandings, similar to those reported in metallic glasses 40–42 and metal−organic framework glasses 43 . The shear bands incline at an angle of ∼50 with respect to the loading direction and contain substantial cavities at sub‐nanoscale as seen in Figure 1D, similar to previous observations in metallic glasses 42,44 .…”

Liquefaction-induced plasticity from entropy-boosted amorphous ceramics

“…35 Moreover, it is worth mentioning that porous films are often observed to exhibit stripping or cracks around the imprint upon indentation especially under a high load (such as those used here). 36,37 The high plasticity of anodic (TiAlV)Ox was further confirmed by the TEM observation of the cross-sectional slices of the indented film (Figures 3 and S9-S11). Note that plasticity could also be evaluated by calculating the percentage change of the film thickness.…”

Bond switching is responsible for nanoductility in zeolitic imidazolate framework glasses

“…1f. Indeed, numerous interesting features of these ZIF glasses have been discovered, such as high Poisson's ratio, 7,17,18 optical transparency, 19 luminescence, 9 and permanent accessible porosity towards H 2 and CO 2 . 12,20 However, to our knowledge, there are only three in-depth studies on their fracture mechanics, with only one non-indentation based study.…”

“…21 The second study based on indentation experiments revealed the occurrence of shear bands on indented faces of ZIF-62 glass. 17 Finally, the third study based on the single-edge precracked beam (SEPB) method discovered that ZIF-62 glass possessed fracture toughness (K Ic ) as low as elastomers or foams (∼0.1 MPa m 0.5 ) and a Young's modulus on the same scale as that of brick and stone, placing the MOF glass in a new area of the Ashby plot. 18 This anomalous position for ZIF-62 glass raises the question about whether all ZIF glasses behave similarly.…”