Atomic structure of hot compressed borosilicate glasses

Linfeng Ding, Kuo Hao Lee, Tongyao Zhao, Yongjian Yang, Michal Bockowski, Benedikt Ziebarth, Qingwei Wang, Jinjun Ren, Morten M. Smedskjaer, John C. Mauro

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Abstract

Borosilicate glasses have been in widespread use for over a century; however, a detailed understanding of the structural response to densification is still lacking. In this work, two commercial borosilicate glasses, viz., SCHOTT N-BK7® (N-BK7) and Borofloat33® (Boro33), are hot compressed up to 2 GPa with nitrogen gas, and the structural response to this densification is explored via 11B solid-state nuclear magnetic resonance (NMR) spectroscopy and classical molecular dynamics (MD) simulations. The molar volume (Vm) of N-BK7 and Boro33 decreases ~5% and ~10%, respectively, as a result of hot compression at 2 GPa. The NMR results demonstrate the presence of three different types of fourfold coordinated boron species (B[4]), which are confirmed in MD simulations to be (Formula presented.) (0B,4Si[4]), (Formula presented.) (1B[3],3Si[4]), and (Formula presented.) (1B[4],3Si[4]) (where subscripts represent different B[4] types and brackets indicate the next nearest neighbors (NNN)). The NMR results also show that the fraction of B[4] increases by ~13% in N-BK7 glass upon hot compression at 2 GPa via the trigonal boron to tetrahedral boron (B[3] to B[4]) conversion, while the fraction of B[4] in Boro33 glass only increases by ~2% at the same pressure, despite the fact that the Vm decrease in N-BK7 is double that of Boro33. The MD simulations capture the experimental trends in B[4] populations, despite an underestimation of the B[4] increase of N-BK7 (only ~6%) at 2 GPa. Moreover, the MD simulations suggest that the Vm reduction is a linear function of bond angle change and the fraction of Si-O-Si and B[4]-O-Si. The modifiers and boron coordination conversion also influence the volume densification of borosilicate glasses by increasing the difficulty of bond bending, decreasing the bond lengths, and increasing the population of B[4]-O-Si linkages. Finally, the B[4] to B[4] conversion, that is, (Formula presented.) (1B[3],3Si[4]) and (Formula presented.) (1B[4],3Si[4]) to (Formula presented.) (0B,4Si[4]), is observed in hot compressed N-BK7 and Boro33 from NMR and qualitatively confirmed in MD.

Original languageEnglish (US)
Pages (from-to)6215-6225
Number of pages11
JournalJournal of the American Ceramic Society
Volume103
Issue number11
DOIs
StatePublished - Nov 1 2020

All Science Journal Classification (ASJC) codes

  • Ceramics and Composites
  • Materials Chemistry

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