High-Energy Mechanical Milling-Driven Reamorphization in Glassy Arsenic Monoselenide: On the Path of Tailoring Special Molecular-Network Glasses

The impact of high-energy milling on glassy arsenic monoselenide g-AsSe is studied with X-ray diffraction applied to diffuse peak-halos proper to intermediate- and extended-range ordering revealed in first and second sharp diffraction peaks (FSDP and SSDP). A straightforward interpretation of this effect is developed within the modified microcrystalline approach, treating “amorphous” halos as a superposition of the broadened Bragg diffraction reflexes from remnants of some inter-planar correlations, supplemented by the Ehrenfest diffraction reflexes from most prominent inter-molecular and inter-atomic correlations belonging to these quasi-crystalline remnants. Under nanomilling, the cage-like As4Se4 molecules are merely destroyed in g-AsSe, facilitating a more polymerized chain-like network. The effect of nanomilling-driven molecular-to-network reamorphization results in a fragmentation impact on the correlation length of FSDP-responsible entities (due to an increase in the FSDP width and position). A breakdown in intermediate-range ordering is accompanied by changes in extended-range ordering due to the high-angular shift and broadening of the SSDP. A breakdown in the intermediate-range order is revealed in the destruction of most distant inter-atomic correlations, which belong to remnants of some quasi-crystalline planes, whereas the longer correlations dominate in the extended-range order. The microstructure scenarios of milling-driven reamorphization originated from the As4Se4 molecule, and its network derivatives are identified with an ab initio quantum-chemical cluster modeling code (CINCA).

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

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.

Letter to the Editor: The extraction of atomic co-ordination numbers from x-ray diffraction data for network glasses

It has been demonstrated that both the detailed electron distributions of the constituent atoms/ions and non-Gaussian Gaussian peaks in T(r) can seriously limit the accuracy of co-ordination numbers extracted from x-ray diffraction data, whether the fit is performed in real or reciprocal space. In general, however, it is preferable to perform the fit in real space, where differences in shape between the experimental and fitted peaks are much more obvious, together with the effect of any experimental uncertainties, as represented by the noise in the resulting correlation function in the region below the first true peak. Note, also, that in reciprocal space the effects of a non-Gaussian peak shape on the extrapolation of the sinusoidal envelope to zero Q, from a high-Q fit to the interference function, Qi(Q), apply equally to neutron diffraction data, similarly limiting the accuracy of the resulting co-ordination numbers.