EXELFS study of the structure of silica and sodium silicate glasses

Abstract

The conventional extended X-ray absorption fine structure (EXAFS) method is not ideal for determining local structure around light elements in a solid. Although the “electron yield” EXAFS technique can be used to increase sensitivity to lighter elements, it is mainly a surface technique. We have employed the extended energy-loss fine structure (EXELFS) technique for determining the local structure (partial radial distribution function, inter atomic distance, and disorder parameter) in oxide glasses, specifically around Si and O in silica and sodium silicate glasses. Because a scanning transmission electron microscope is used, EXELFS also allows high spatial resolution which is particularly useful for a glass prone to phase separation.EXELFS results from the same phenomenon responsible for EXAFS, namely the interference of the outgoing spherical wave of the ejected electron with portions of itself which have been backscattered from the neighboring atoms in the solid. This produces oscillations in intensity beyond the absorption edge. These variations in intensity are transformed to radial distribution functions in the same fashion as EXAFS data. EXELFS, like EXAFS, provides local atomic environment information that is element specific.