Topologically Ordered Amorphous Silica Obtained from the Collapsed Siliceous Zeolite, Silicalite-1-F: A Step toward "Perfect" Glasses

A dense amorphous form of silica was prepared, at high pressure from the highly compressible, siliceous zeolite, silicalite-1-F. Reverse Monte Cado modeling of total X-ray scattering data shows that the structure of this novel amorphous form Of SiO2 recovered under ambient conditions is distinct from vitreous SiO2 and retains the basic framework topology (i.e., chemical bonds) of the starting crystalline zeolite. This material is, however, amorphous over the different length scales probed by Raman and X-ray scattering due to strong geometrical distortions. This is thus an example of new topologically ordered, amorphous material with a different intermediate-range structure, a lower entropy with respect to a standard glass, and distinct physical and mechanical properties, eventually approaching those of an "ordered" or "perfect" glass. The same process in more complex aluminosilicate zeolites will, in addition, lead to an amorphous material which conserves the framework topology and chemical order of the crystal. The large volume collapse in this material may also be of considerable interest for new applications in shock wave absorption.