31P and 29Si NMR study of sol–gel-synthesized phosphate ceramics

Silicophosphates containing SiO6octahedra – anhydrous synthesis under ambient conditions

“…The authors assumed in the case of TEOS a (Si 2 P 2 C 4 H 12 O 11 ) n -structure with alternating Si-O and P-O units based on the analytical data. Two publications from 1998 45,46 report similar results for the direct reaction of phosphorus pentoxide and TEOS. In these papers the authors report that the mixture was refluxed as well at the corresponding boiling point for 12 h. The synthesized P-Si sols show no octahedral environment in the 29 Si NMR spectrum.…”

Multinuclear NMR study of phosphosilicate gels derived from POCl3 and Si(OC2H5)4

“…Yet these chemical shifts cannot distinguish between Si-O-P or P-O-P, thus the phosphorus may be self-polymerizing or cross-linking into the framework. Characteristic 31 P chemical shifts for Si-O-P phases were seen in the previous samples at À44 ppm [8], but these are from crystalline materials such as the Si 5 O(PO 4 ) 6 phase [26][27][28] which the intention was to avoid. Clearer evidence for Si-O-P bonds can, in principle, be found in the 29 Si NMR data.…”

Investigations on sol–gel process and structural characterization of SiO2-P2O5 powders

“…Broad components in 31 P MAS NMR corresponding to condensed P\O\Si species were observed in the case of heat treated gels and aerogels. Wang et al [17,30] observed also broad 31 P resonances in the same chemical shift regions but made the assumption that such resonances could be assigned to P\O\P bonds (i.e. pyrophosphate groups).…”