Heterogeneities in glasses and small-angle scattering methods

The systematic study of heterogeneities in glasses is important both from the theoretical side (fluctuations in supercooled liquids) and for practical applications: fibre optics for optical communications systems and kinetics of phase separation and crystallization for synthesis of glass ceramics. Texture brought about by phase separation in glasses is in the range of 100-10000 Å which makes it particularly well suited for small-angle scattering studies. A review is presented of results obtained in this way for glassy systems according to their position in the immiscibility field : evaluation of (a) discrete precipitates in the case of a minor phase precipitation and (b) dense interconnected structures such as can be generated by a spinodal mechanism. Comparison is made with the results obtained by electron microscopy and first results obtained by small-angle scattering of neutrons.