Structural investigations of celsian glass derived from Ba-LTA zeolite

The structure of stoichiometric celsian glass was investigated by Si-29 MAS NMR and IR spectroscopies and reverse Monte Carlo (RMC) simulation of X-ray diffraction data. The glass was prepared by thermally induced phase transformation of Ba2+-exchanged LTA (Linde Type A) zeolite, under annealing conditions prior to hexacelsian crystallization. NMR and IR measurements have shown that the local silicon-aluminium ordering of the starting zeolite framework, as well as the framework fragments in the form of deformed tetrahedral rings, is retained in the glass structure. Interatomic distances and mean coordination numbers were calculated from the three-dimensional RMC derived structure model. The local Ba2+ environment in the glass was compared with the corresponding crystalline polymorphs. Ba-O distances in the glass are longer than the distances in hexacelsian but the coordination number 12.00 and the increase in the Ba-T distance, compared to zeolite, indicate the establishment of hexacelsian-like coordination. Inspection of the three-dimensional RMC model of the glass showed a layered structure, with Ba2+ cations between the layers.