Influence of rare-earth ions on SiO2-Na2O-RE2O3 glass structure

Praseodymium and europium sodium silicate glasses of nominal composition (SiO2)(0.70-x)(Na2O)(0.30)(RE2O3)(x), where RE is the rare earth and 0 <= x <= 0.10, were studied by neutron and high-energy x-ray scattering and classical molecular dynamics simulations. The observation of a significant x-ray intensity in doped as compared to un-doped glasses is indicative of RE-RE correlations at a distance of similar to 3.7-3.9 angstrom, much shorter than would be expected for a homogeneous distribution, suggesting that clustering of the rare-earth cations occurs in both these glass systems at low concentrations. Above x = 0.075 (nominal), minimal changes in this region indicate that the RE atoms are incorporated much more randomly into the glass structure. The molecular dynamics simulations suggest that the rare-earth ions enter the sodium-rich regions in the sodium silicate glasses and act as modifiers. A cluster analysis performed on the model systems indicates that the tendency for clustering is higher in praseodymium-containing glasses than in the europium glasses.