XANES OF SIXFOLD SILICON IN MOO3-SIO2-P2O5 GLASSES

Glasses of the ternary MoO3-SiO2-P2O5 system have been prepared by mel t quenching in air and studied using Si K-edge X-ray absorption near-e dge structure (XANES) spectroscopy to estimate proportion of sixfold c o-ordinated silicon. Sixfold Si is detectable in most glasses prepared with molar (MoO3 + SiO2) > P2O5. The proportion of sixfold Si increas es from 0% to 49% of total Si atoms with increase in P2O5 content. Our results indicate, for the first time, the presence of sixfold Si in a lkali- and alkaline-earth-free silicophosphate ternary glasses, and st rongly favor the view that alkali and alkaline-earth modifiers are not necessary to stabilize sixfold Si in silicophosphate glasses. In tern ary MoO3-SiO2-P2O5 composition space, isopleths of proportion of sixfo ld Si trend parallel to the MoO3-SiO2 join and indicate that the terna ry glass structure is comprised of separate molybdophosphate and silic ophosphate entities. (C) 1998 Elsevier Science B.V. All rights reserve d.