Medium range order around cations in silicate glasses

In multicomponent silicate glasses, chemically selective techniques are needed to probe the local environment of specific cations. This paper reviews recent results obtained using three methods which give access to this chemical selectivity: extended X-ray absorption fine structure (EXAFS), anomalous wide-angle X-ray scattering (AWAXS) and neutron scattering with isotopic substitutions (NSIS) in glasses, These methods allow us to determine the relationships between cation sites and the glassy network. Scattering methods give structural information around cations up to 10 Angstrom and demonstrate the existence of a local order around densely packed cations, indicating a non-random distribution of these cations in silicate glasses, These data may be used to constrain glass structure using modified Pauling rules and aid a better understanding of the macroscopic properties of silicate glasses.