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1 ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK
2 Department of Earth Sciences, Cambridge University, Downing Street, Cambridge CB2 3EQ, UK
* E-mail: d.a.keen{at}rl.ac.uk
The structure of amorphous silica has frequently been compared with its crystalline counterparts in an attempt to understand the glass structure beyond short-range correlations. This paper presents results from neutron total scattering measurements of several polymorphs of silica and shows how these can be used to make a direct, quantitative comparison of amorphous and crystalline forms. It is found that the glass is similar to HP-tridymite and ß-cristobalite, both dynamically-disordered crystalline phases of silica, but only out to distances ~7.5 Å, beyond which the structures diverge. This is too small to validate a microcrystallite theory of glass structure. It is the average 180° Si–O–Si linkage in these two crystalline phases which gives them the flexibility for their instantaneous disordered structure to resemble the quenched (static) glass structure.
KEYWORDS: total scattering, silica polymorphs, amorphous silica, glass
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