Structural changes in sodium tetrasilicate glass around the liquid-glass transition: a neutron diffraction study

The structure of sodium tetrasilicate (Na2-Si4O9) glass and melt was studie d in the range from 300 to 950 K by neutron diffraction. Increasing tempera ture leads to gradual decrease of the peak intensities in the static struct ure factors possibly with a change in the slope at the glass transition tem perature (T(g)congruent to 773 K), but no shift and broadening of the peaks is observed. Especially, the position of the first sharp diffraction peak (FSDP) at 1.6 Angstrom(-1) remains constant in the whole temperature range studied. The corresponding pair correlation functions g(r) are very similar at all temperatures: Only a slight broadening of the Si-O and O-O first ne arest-neighbour peaks with temperature is observed, which can be attributed to temperature enhanced dynamic distortions of the SiO4 tetrahedra. All th ese results suggest that there is little change not only in the short- but also in the medium-range order of the sodium tetrasilicate glass and melt a round the glass-liquid transition.