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

J Kalahe and XN Lu and JD Vienna and BJ Riley and JC Du, PHYSICS AND CHEMISTRY OF GLASSES-EUROPEAN JOURNAL OF GLASS SCIENCE AND TECHNOLOGY PART B, 65, 161-176 (2024).

DOI: 10.13036/17533562.65.5.14

The structures and properties of two series of sodium iron phosphate glasses: 70P(2) O-5.(30-x)Fe-2 O-3.xNa(2) O (P70 series) and (100-x)0 & sdot;7P(2) O-5.0 & sdot;3Fe(2) O-3. xNa(2) O (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 Q(n) 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 Fe-2 O-3 for the P70 series, while it remained relatively the same for the P/Fe=7/3 series. Meanwhile P 5+ 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 Fe-2 O-3 as a conditional glass former, the glass network became more polymerised with increasing Fe-2 O-3 content, as shown by the formation of Q(4) phosphate units. For P70 glasses, an enhanced glass network was achieved by eliminating lower Q(n) species with increasing Fe-2 O-3 content, eventually reaching a maximum of Q(3) species. The effect of Fe-2 O-3, despite its relatively small variation in the concentration (24-28 & sdot;5 mol%), in P/Fe=7/3 glasses, ensures that Q(4) species consistently surpass Q(3) 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 F-net and its variations were used. The modified F-net, BS-dm (bond strength in diatomic molecules), BS-dc (bond strength in diatomic cations), and E-F (enthalpy of fusion) showed an excellent linear correlation with density, with R-2 values ranging from 0 & sdot;820 to 0 & sdot;993. At the same time, the best descriptors for bulk, shear, and Young's moduli were found to be F-net with BS-dc. This study provides valuable insights into firstly the structures of P-2 O-5 -Fe-2 O-3 -Na-2 O glasses as a function of Fe-2 O-3 and Na-2 O concentration, and secondly the structure-property relationships of these glasses, which will help future design of glass compositions for technological applications.

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