The synthesis of P2O5-SiO2 glasses from solutions has been studied thr
ough gelation kinetics, Raman and nuclear magnetic resonance (NMR) spe
ctroscopies. Different preparation methods are compared. The effect of
the phosphorus precursor has been investigated. Phosphoric acid ester
s are not hydrolyzed and they do not yield condensation with silica. R
eaction of anhydrous H3PO4 with Si-OR groups leads to the formation of
Si-O-P bonds which are easily hydrolyzed. Only a few remain after add
ition of water and gelation. Therefore, P-Si homogeneity is difficult
to achieve after gelation and the following drying and heat-treatment
procedures. This absence of homogeneity is observed by solid-state mag
ic angle spinning (MAS)-NMR and X-ray diffraction studies performed on
gel samples heated at 300, 500 and 800 degrees C in the case of xerog
els and 500, 950 and 1140 degrees C for aerogels.