Abstract
The structure of calcium aluminosilicate glasses (CaO)x(Al2O3)y(SiO2)1−x−y with the near tectosilicate compositions x ≃ 0.19 and 1 − x − y ≃ 0.61 or x ≃ 0.26 and 1 − x − y ≃ 0.49 was investigated by in situ high-pressure neutron diffraction and 27Al nuclear magnetic resonance (NMR) spectroscopy. The results show three distinct pressure regimes for the transformation of the aluminum coordination environment from tetrahedral to octahedral, which map onto the deformations observed in the production of permanently densified materials. The oxygen packing fraction serves as a marker for signaling a change to the coordination number of the network forming motifs. For a wide variety of permanently densified aluminosilicates, the aluminum speciation shares a common dependence on the reduced density ρ′ = ρ/ρ0, where ρ is the density and ρ0 is its value for the uncompressed material. The observed increase in the Al-O coordination number with ρ′ originates primarily from the formation of six-coordinated aluminum Al(VI) species, the fraction of which increases rapidly beyond a threshold ρ thr ′ ∼ 1.1. The findings are combined to produce a self-consistent model for pressure-induced structural change. Provided the glass network is depolymerized, one-coordinated non-bridging oxygen atoms are consumed to produce two-coordinated bridging oxygen atoms, thus increasing the network connectivity in accordance with the results from 17O NMR experiments. Otherwise, three-coordinated oxygen atoms or triclusters appear, and their fraction is quantified by reference to the mean coordination number of the silicon plus aluminum species. The impact of treating Al(VI) as a network modifier is discussed.
| Original language | English |
|---|---|
| Article number | 074503 |
| Journal | Journal of Chemical Physics |
| Volume | 161 |
| Issue number | 7 |
| Early online date | 16 Aug 2024 |
| DOIs | |
| Publication status | Published - 16 Aug 2024 |
Data Availability Statement
The datasets created during this research are openly available from the University of Bath Research Data Archive at https://doi.org/10.15125/BATH-01387.107 The D4c diffraction datasets are available from Ref. 108, and the PEARL data sets are available from Ref. 109.Acknowledgements
We acknowledge Hesameddin Mohammadi (Bath), Claude Payre (Grenoble), and Alain Bertoni (Grenoble) for help with the D4c experiments, Nicholas Funnell (ISIS) for help with the PEARL experiment, and Sandro Jahn (Köln) for the datasets from Ref. 11.Funding
L.V.D.G. acknowledges funding and support from the EPSRC Center for Doctoral Training in Condensed Matter Physics (CDT-CMP) under Grant No. EP/L015544/1, the Science and Technology Facilities Council (STFC), and Diamond Light Source Ltd. (Reference No. STU0173). A.Z. was supported by a Royal Society-EPSRC Dorothy Hodgkin Research Fellowship. P.S.S. and A.Z. are grateful to Corning Inc. for the award of Gordon S. Fulcher Distinguished Scholarships during which this work was conceived. We acknowledge the use of the Inorganic Crystal Structure Database, accessed via the Chemical Database Service funded by the Engineering and Physical Sciences Research Council (EPSRC) and hosted by the Royal Society of Chemistry. P.S.S. and A.Z. designed the diffraction project on the glass structure. R.E.Y. performed the NMR experiments and analyzed the results. L.V.D.G., P.S.S., C.L.B., and H.E.F. performed the neutron diffraction experiments, and L.V.D.G. analyzed the results. P.S.S. and L.V.D.G. developed the model, and P.S.S. processed the data. P.S.S. wrote the paper with input from all co-authors.
ASJC Scopus subject areas
- General Physics and Astronomy
- Physical and Theoretical Chemistry