We determine the mechanism of the initiation of Al−O(H) bond breaking for zeolitic structures mordenite (MOR), faujasite (FAU), MFI, and chabazite (CHA) with high Si/Al ratio occurring during dealumination. Periodic density functional theory calculations demonstrate that water adsorption on the Al atom takes place in anti position to the Brønsted acid site, via a penta-or tetracoordinated Al species. A subsequent 1,2-dissociation of water on adjacent framework oxygen atoms leads to the first Al−O(H) bond breaking (with activation energies of ∼76−125 kJ/mol). A Brønsted−Evans−Polanyi relationship to estimate transition states (TS) is established and opens the door to predictions of which crystallographic sites are able to initiate dealumination.

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The possibility to synthesize GeSe4 glass by mechanical alloying followed by sintering has been demonstrated. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analysis have been performed on the powder as a function of milling duration in order to follow the amorphization process of raw metallic germanium and selenium elements. Completely amorphous powder has been sintered using a homemade hot press. Optical transmission and the density of the final bulk material have been studied.

'Cold' crystallization in 80GeSe2-20Ga2Se3 chalcogenide glass nanostructurized due to thermal annealing at 380°C for 10, 25, 50, 80, and 100 h are probed with X-ray diffraction, atomic force, and scanning electron microscopy, as well as positron annihilation spectroscopy performed in positron annihilation lifetime and Doppler broadening of annihilation line modes. It is shown that changes in defect-related component in the fit of experimental positron lifetime spectra for nanocrystallized glasses testify in favor of structural fragmentation of larger free-volume entities into smaller ones. Nanocrystallites of Ga2Se3 and/or GeGa4Se8 phases and prevalent GeSe2 phase extracted mainly at the surface of thermally treated samples with preceding nucleation and void agglomeration in the initial stage of annealing are characteristic features of cold crystallization.

Positron annihilation lifetime spectroscopy combined with Doppler broadening of annihilation radiation was applied to study free-volume entities in GeS2-Ga2S3glasses affected by Ga additions. It is shown that Ga-related void sub-system plays a decisive role in positron trapping process, while the overall density variation is defined mainly by Ge-related sub-system. These results serve as basis for new characterization route for inner free-volume structure of these glasses.