Influence of P2O5 content on the structure of SiO2-Na2O-CaO-P2O5 bioglasses by 29Si and 31P MAS-NMR

29Si and 31P MAS-NMR has been used in order to study the influence of P2O5 content on the structure of SiO2-Na2O-CaO-P2O5 bioglasses. The 29Si NMR spectra show many QSin entities co-existing in the same glass. For all the glasses, the QSin species are associated with Ca2+ and Na+. The glass network becomes more and more polymerized when the P2O5 content increases. The 31P NMR spectra show that the phosphorus is present as monophosphate with or without diphosphate complexes associated with both Ca2+ and Na+. The increase in phosphorus content modifies the relative abundance of phosphate complexes and leads to changes in the chemical environment around phosphate indicating that the distribution of cations is not homogeneous. Indeed most phosphate complexes attract calcium. The percentage of diphosphate complexes increases with the P2O5 content as the silicate network repolymerizes.