Structure and structure–property relationships in sodium iron phosphate glasses from molecular dynamics simulations and QSPR analysis

The structures and properties of two series of sodium iron phosphate glasses: 70P2O5.(30−x)Fe2O3.xNa2O (P70 series) and (100−x)[0·7P2O5.0·3Fe2O3].xNa2O (P/Fe=7/3 series), were studied by using molecular dynamics (MD) simulations with effective partial charge potentials. Structural analyses of bond lengths, coordination numbers, bond angles and Qn distributions were performed and compared to experiments and other simulation results. It was found that the cation–oxygen bond lengths were in good agreement with the experiments. The coordination number of Fe3+ decreased with increasing Fe2O3 for the P70 series, while it remained relatively the same for the P/Fe=7/3 series. Meanwhile P5+ remains four-fold coordinated in both glass series. Considerable structural changes were observed as the composition was varied in these two series of glasses. Considering Fe2O3 as a conditional glass former, the glass network became more polymerised with increasing Fe2O3 content, as shown by the formation of Q4 phosphate units. For P70 glasses, an enhanced glass network was achieved by eliminating lower Qn species with increasing Fe2O3 content, eventually reaching a maximum of Q3 species. The effect of Fe2O3, despite its relatively small variation in the concentration (24–28·5 mol%), in P/Fe=7/3 glasses, ensures that Q4 species consistently surpass Q3 species throughout the examined glasses. Several properties, such as Young’s, shear and bulk moduli, were calculated, and their changes with composition and relation to the glass structure were discussed. Furthermore, together with two other recently studied series of glasses, Quantitative Structure–Property Relationship analysis of over 30 glasses in the ternary glass system was performed using the structural data from MD simulations. The structural descriptor Fnet and its variations were used. The modified Fnet, BS-dm (bond strength in diatomic molecules), BS-dc (bond strength in diatomic cations), and EF (enthalpy of fusion) showed an excellent linear correlation with density, with R2 values ranging from 0·820 to 0·993. At the same time, the best descriptors for bulk, shear, and Young’s moduli were found to be Fnet with BS-dc. This study provides valuable insights into firstly the structures of P2O5–Fe2O3–Na2O glasses as a function of Fe2O3 and Na2O concentration, and secondly the structure–property relationships of these glasses, which will help future design of glass compositions for technological applications.