Statistical mechanical model for the formation of octahedral silicon in phosphosilicate glasses

Mikkel L. Bødker, Johan B. Pedersen, Francisco Muñoz, John C. Mauro, Morten M. Smedskjaer*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

4 Citations (Scopus)


Unlike ambient pressure silicate glasses, some phosphosilicate glasses contain sixfold-coordinated silicon (Si6) units even when prepared at ambient pressure. The variation in the fraction of Si6 with composition remains a topic of interest, both for technological applications of phosphosilicate glasses and for fundamental understanding of the glass structure. In this work, we use statistical mechanical modeling to predict the composition–structure relationships in Na2O–P2O5–SiO2 and CaO–P2O5–SiO2 glasses. This is achieved by accounting for the enthalpic and entropic contributions to the interactions between each pairwise modifier ion and structural unit. The initial enthalpy parameters are obtained based on experimental structural data for binary Na2O–SiO2, CaO–SiO2, Na2O–P2O5, and CaO–P2O5 glasses, which can then be transferred to predict the structure of mixed former glasses. This approach has previously been used to predict the short-range structure of borosilicate and aluminoborate glass systems. However, here we show that the formation of Si6 must be specifically included to make accurate predictions of the composition–structure relationships in phosphosilicate glasses. After incorporating the formation mechanism of Si6 in the statistical mechanics model, we find an excellent agreement between model predictions and experimental structure data for Na2O–P2O5–SiO2 and CaO–P2O5–SiO2 glasses.

Original languageEnglish
JournalJournal of the American Ceramic Society
Issue number2
Pages (from-to)1031–1038
Number of pages8
Publication statusPublished - Feb 2022

Bibliographical note

Funding Information:
This work was supported by the Independent Research Fund Denmark (grant no. 7017‐00019) to M.M.S. and the Elite Research Travel Grant to M.L.B. by the Danish Ministry of Higher Education and Science (grant no. 9095‐00019A).

Publisher Copyright:
© 2021 The American Ceramic Society


  • glass
  • modeling/model
  • structure


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