Sol–gel produced sodium calcium phosphosilicates for bioactive applications: Synthesis and structural characterisation

A series of phosphosilicates P2O5 (45 mol%)–CaO (20–40 mol%)–Na2O (5–20 mol%)–SiO2 (10–15 mol%) has been synthesised by the sol–gel route using PO(OH)3−x(OC2H5)x (x = 1, 2) as the phosphorus precursor. Evolution of the gels with temperature was studied using thermogravimetric analysis and differential thermal analysis. These phosphosilicates show good stability against crystallisation remaining fully amorphous even after calcination at 400 °C. The short-range structure of the stabilised sol–gel glasses and the effect of adding modifier oxides to the network structure have been investigated using a combination of techniques: FT-IR spectroscopy, 31P magic angle spinning NMR, high energy XRD and P L-edge XANES.