Pressure induced structural transformations in amorphous MgSiO3 and CaSiO3

Philip S Salmon, Gregory S Moody, Yoshiki Ishii, Keiron J Pizzey, Annalisa Polidori, Mathieu Salanne, Anita Zeidler, Michela Buscemi, Henry E Fischer, Craig L. Bull, Stefan Klotz, Richard Weber, Chris J Benmore, Simon G MacLeod

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Abstract

The pressure-induced structural transformations in metasilicate MSiO3 glass (M = Mg or Ca) on cold-compression from ambient pressure to 17.5 GPa were investigated by neutron diffraction. The structure of the glass recovered to ambient conditions from a pressure of 8.2 or 17.5 GPa was also investigated by neutron or X-ray diffraction. The experimental work was complemented by molecular dynamics simulations using a newly-developed aspherical ion model. The results show network structures based predominantly on corner-sharing tetrahedral SiO4 units. At pressures up to ~8 GPa, there is little change to the network connectivity as described by the Qn speciation, where n denotes the number of bridging oxygen (BO) atoms per SiO4 tetrahedron. On compression of the glass to 17.5 GPa, the Mg–O coordination number increases from 4.5(1) to 6.2(1), and the Ca–O coordination number increases from 6.15(17) to 7.41(7). In both cases, the increased M-O coordination numbers are accompanied by an increased fraction of M-BO versus M-NBO connections, where NBO denotes a non-bridging oxygen atom. The results give the fraction of triple-bridging oxygen atoms as ~0.5% at 17.5 GPa, which does not support the formation of a substantial fraction of oxygen triclusters in either glass. The M-O coordination number of the recovered glass is larger than for the uncompressed material, which originates from an increased fraction of M-BO connections, and increases with the pressure from which the glass is recovered. The results suggest that the measured decrease in viscosity of molten MSiO3 on pressure increasing from ambient to ~8 GPa is not related to a large change in network polymerization, but to the appearance of higher-coordinated M-centred polyhedra that contain a larger fraction of weaker M-BO bonds.
Original languageEnglish
Article number100024
Pages (from-to)1-14
Number of pages14
JournalJournal of Non-Crystalline Solids X
Volume3
Early online date10 May 2019
DOIs
Publication statusPublished - 1 Sep 2019

Keywords

  • Glass structure
  • Molecular dynamics
  • Neutron diffraction
  • Pressure
  • X-ray diffraction

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Condensed Matter Physics
  • Materials Chemistry

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  • Cite this

    Salmon, P. S., Moody, G. S., Ishii, Y., Pizzey, K. J., Polidori, A., Salanne, M., Zeidler, A., Buscemi, M., Fischer, H. E., Bull, C. L., Klotz, S., Weber, R., Benmore, C. J., & MacLeod, S. G. (2019). Pressure induced structural transformations in amorphous MgSiO3 and CaSiO3. Journal of Non-Crystalline Solids X, 3, 1-14. [100024]. https://doi.org/10.1016/j.nocx.2019.100024