Abstract:

Magic angle spinning NMR was used to study SiO2.P2O5 glass to det. if Si transitions from 4-fold (IV) to 6-fold coordination impose a barrier to nucleation. Results indicate that the glass contains only Si(IV) which, on devitrification at ambient pressures, transforms to cryst. Si phosphate with Si(IV). The 4- to 6-fold transition does not prohibit nucleation of the cryst. phase, indeed, the phase contg. only Si(IV) appears to nucleate 1st. The presence of only tetrahedral coordination in the glass is consistent with Zachariasen's prediction.