NA-RAY-DIFFRACTION( COORDINATION IN SODIUM DIBORATE AND TRIBORATE GLASSES BY X)

Na+ coordination in diborate (Na2O-2B2O3) and triborate (Na2O-3B2O3) g lasses was investigated by X-ray diffraction through a difference meth od in which radial distribution functions of lithium borate samples ar e subtracted from those of sodium borate glasses of the same molar com position. The difference curves exhibited peaks arising from the distr ibution of nearest neighbour O atoms around Na+ ions. The quantitative analysis of these peaks and a careful evaluation of the reliability o f structural parameters were performed. Average coordination numbers w ere 4.0+/-0.4 for diborate and 4.8+/-0.5 for triborate. Finally, a com parison was made of Na+ environments in glasses and crystals of equal composition, and the similarities and the differences were discussed.