EXAFS STUDIES OF THE EFFECT OF GLASS COMPOSITION ON THE COORDINATION OF TRIVALENT CHROMIUM IN GLASSES IN THE SYSTEM NA2O-AL2O3-SIO2

A recent study of the epr and optical characteristics of Cr3+ [Hollis et al., submitted to Phys, Chem, Glasses; Hollis and Harris, submitted to Phys. Chem, Glasses] has shown the importance of nearest neighbour and second nearest neighbour coordination of the Cr3+ in determining optical absorption and fluorescence parameters. In this study, station 8.1 of the Daresbury S.R.S., UK was used to determine the near neighb our environment of these glasses, The results show clear evidence that the next nearest neighbours to the chromium are affected by the phase field of the system Na2O-Al2O3-SiO2 to which any particular glass belo ngs. This systematic behaviour follows that of the optical and epr par ameters observed in the previous study [Hollis et al., submitted to Ph ys. Chem. Glasses: Hollis and Harris, submitted to Phys. Chem. Glasses ]. This result implies that a non-random structure of the glass exists in the nearest and next nearest neighbour coordination spheres of the chromium, A significant effect on the optical properties of trivalent chromium is produced by the site distortions at the chromium ion [Hol lis et al., submitted to Phys. Chem. Glasses; Hollis and Harris, submi tted to Phys. Chem. Glasses]. These distortions in turn result from th e packing of the nest nearest neighbours, which are studied here. (C) 1997 Published by Elsevier Science B.V.