X-ray absorption spectroscopy studies of glass structure

In the last few decades, X-ray Absorption Spectroscopy (XAS) has recorded a remarkable amount of interest in the study of glass structure for its sensitivity to the Short Range Order (SRO) around a selected atomic species. XAS greatest evolution started in the seventies of the last century thanks to an adequate and structurally useful theoretical interpretation of the Extended X-ray Absorption Fine Structure (EXAFS) beyond the absorption edge and to the contemporaneous advent of synchrotron radiation facilities. EXAFS probes the local structure of liquid, vitreous, amorphous, and crystalline materials; it is particularly important for noncrystalline systems since they do not give rise to the Bragg diffraction. EXAFS is also used to determine the local environment of impurities contained in glasses, even if they are very diluted. Today, a reliable theoretical description of glassy system structure through modern modelling techniques should be carried out on the basis of x-ray and/or neutron scattering patterns, along with a careful use of the information derived from SRO techniques like EXAFS, NMR, etc. The use of EXAFS in the case of nanocrystalline glass-ceramic systems is very important, since the obtained information are complemental to the ones determined by the Bragg diffraction. The paper gives a brief description of EXAFS theory and analysis methods in the case of disordered systems. Examples of state-of-the-art studies in different glassy systems will be presented along with a critical assessment of EXAFS potential for such systems.