UCL Discovery

Abstract

First principles molecular dynamics simulations of ternary phosphate-based glasses P2O5-CaO-Na2O (PBGs) have been carried out in order to provide an accurate description of the local structure and properties of these important materials for biomedical applications. The structures of PBGs with compositions (P2O5)(0.45)(CaO)(x)(Na2O)(0.55-x) (x = 0.30, 0.35, and 0.40) were generated using a full ab initio molecular dynamics melt-and-quench procedure. The analysis of the structure of the glasses at 300 K shows the prevalence of the meta phosphate Q(2) and pyrophosphate Q(1) species, whereas the number of Q(3) units, which constitute the three-dimensional phosphate network, significantly decreases with the increase in calcium content in the glass. Calculation of the pair and angular distribution functions suggests that the rigidity of the phosphate tetrahedral glass network increases with the concentration of calcium, an observation which is interpreted in terms of the tendency of Ca2+ to be a stronger coordinator than sodium.