中国物理B ›› 2026, Vol. 35 ›› Issue (5): 56102-056102.doi: 10.1088/1674-1056/ae3606

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Free oxide ion abundances in Na, Ba, and K silicate glasses from O 1s XPS, 29Si NMR, Raman, and MD simulations

G. Michael Bancroft1,†, H. Wayne Nesbitt2, John S. Tse3, Grant S. Henderson4, and Ben J. A. Moulton5   

  1. 1 Department of Chemistry, University of Western Ontario, London, ON N6A 5B7 Canada;
    2 Department of Earth Sciences, University of Western Ontario, London, ON N6A 5B7 Canada;
    3 Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, SASK S7N 5E2 Canada;
    4 Department of Earth Sciences, University of Toronto, Toronto, ON M5S 3B1 Canada;
    5 Inamori School of Engineering, New York College of Ceramics, Alfred University, Alfred, New York 14802 USA
  • 收稿日期:2025-10-23 修回日期:2026-01-06 接受日期:2026-01-09 发布日期:2026-05-11
  • 通讯作者: G. Michael Bancroft E-mail:gmbancro@uwo.ca

Free oxide ion abundances in Na, Ba, and K silicate glasses from O 1s XPS, 29Si NMR, Raman, and MD simulations

G. Michael Bancroft1,†, H. Wayne Nesbitt2, John S. Tse3, Grant S. Henderson4, and Ben J. A. Moulton5   

  1. 1 Department of Chemistry, University of Western Ontario, London, ON N6A 5B7 Canada;
    2 Department of Earth Sciences, University of Western Ontario, London, ON N6A 5B7 Canada;
    3 Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, SASK S7N 5E2 Canada;
    4 Department of Earth Sciences, University of Toronto, Toronto, ON M5S 3B1 Canada;
    5 Inamori School of Engineering, New York College of Ceramics, Alfred University, Alfred, New York 14802 USA
  • Received:2025-10-23 Revised:2026-01-06 Accepted:2026-01-09 Published:2026-05-11
  • Contact: G. Michael Bancroft E-mail:gmbancro@uwo.ca

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摘要： In alkali silicate glasses with $\le 50$ mol% $M_{2}$O ($M={\rm Na}$, K, Rb, Cs), the existence of $>1$ mol% reactive ``free'' oxide (FO, where O is not bonded to Si) has been a highly controversial topic over the past 15 years. Unlike their crystalline analogues, Raman and $^{29}$Si nuclear magnetic resonance (NMR) studies since 1980 have shown that two or more $Q^{n}$ ($n=$0-4) species are present in silicate glasses over a wide range of compositions. For example, $M_{2}$SiO$_{3}$ crystals contain only $Q^{2}$ species; however, glasses of the same composition exhibit $Q^{1}$ and $Q^{3}$ in addition to $Q^{2}$. Previous Raman and NMR studies on alkali silicate glasses have related the abundances of these three species solely through disproportionation reactions (e.g. $2{ Q}^{2}\Leftrightarrow { Q}^{1}+{ Q}^{3}$). In doing so, polymerization reactions (e.g. $2{ Q}^{2}\Leftrightarrow 2{ Q}^{3}+{\rm FO}$) were completely neglected. By combining published O 1s x-ray photoelectron spectroscopy (XPS) spectra, $^{29}$Si NMR and Raman results for 40 mol% and 50 mol% Na$_{2}$O, K$_{2}$O, and BaO glasses, together with new molecular dynamics (MD) simulations of Na$_{4}$SiO$_{4}$ glass, we provide consistent and compelling evidence for the existence of $>1$ mol% FO in these glasses and melts. In particular, for 50 mol% K$_{2}$O silicate glass, all three experimental techniques estimate FO to be $\ge 7$ mol%, while MD simulations of Na$_{4}$SiO$_{4}$ yield $\sim 5$ mol% FO. Our analysis requires revised assignments (challenging decades of ``conventional wisdom'') for $^{29}$Si NMR and Raman spectra, based on O mass balance, recognition of M-BO bonding effects first identified in O 1s XPS spectra, and quantitative analysis of Raman spectra for 40-50 mol% Na$_{2}$O, K$_{2}$O, and BaO glasses. These FO values are comparable to those now accepted for alkaline-earth silicate glasses. The importance of this reactive FO for chemical reactivity (e.g. with H$_{2}$O and CO$_{2}$), bioactivity, and physical properties (e.g. melting) of silicate glasses is discussed.

关键词: alkali silicate glasses, free oxide (Na-O-Na), O 1s XPS, Raman, $^{{29}}$Si NMR

Abstract: In alkali silicate glasses with $\le 50$ mol% $M_{2}$O ($M={\rm Na}$, K, Rb, Cs), the existence of $>1$ mol% reactive ``free'' oxide (FO, where O is not bonded to Si) has been a highly controversial topic over the past 15 years. Unlike their crystalline analogues, Raman and $^{29}$Si nuclear magnetic resonance (NMR) studies since 1980 have shown that two or more $Q^{n}$ ($n=$0-4) species are present in silicate glasses over a wide range of compositions. For example, $M_{2}$SiO$_{3}$ crystals contain only $Q^{2}$ species; however, glasses of the same composition exhibit $Q^{1}$ and $Q^{3}$ in addition to $Q^{2}$. Previous Raman and NMR studies on alkali silicate glasses have related the abundances of these three species solely through disproportionation reactions (e.g. $2{ Q}^{2}\Leftrightarrow { Q}^{1}+{ Q}^{3}$). In doing so, polymerization reactions (e.g. $2{ Q}^{2}\Leftrightarrow 2{ Q}^{3}+{\rm FO}$) were completely neglected. By combining published O 1s x-ray photoelectron spectroscopy (XPS) spectra, $^{29}$Si NMR and Raman results for 40 mol% and 50 mol% Na$_{2}$O, K$_{2}$O, and BaO glasses, together with new molecular dynamics (MD) simulations of Na$_{4}$SiO$_{4}$ glass, we provide consistent and compelling evidence for the existence of $>1$ mol% FO in these glasses and melts. In particular, for 50 mol% K$_{2}$O silicate glass, all three experimental techniques estimate FO to be $\ge 7$ mol%, while MD simulations of Na$_{4}$SiO$_{4}$ yield $\sim 5$ mol% FO. Our analysis requires revised assignments (challenging decades of ``conventional wisdom'') for $^{29}$Si NMR and Raman spectra, based on O mass balance, recognition of M-BO bonding effects first identified in O 1s XPS spectra, and quantitative analysis of Raman spectra for 40-50 mol% Na$_{2}$O, K$_{2}$O, and BaO glasses. These FO values are comparable to those now accepted for alkaline-earth silicate glasses. The importance of this reactive FO for chemical reactivity (e.g. with H$_{2}$O and CO$_{2}$), bioactivity, and physical properties (e.g. melting) of silicate glasses is discussed.

Key words: alkali silicate glasses, free oxide (Na-O-Na), O 1s XPS, Raman, $^{{29}}$Si NMR

中图分类号: 

  • 61.43. Fs
79.60.-i (Photoemission and photoelectron spectra) 76.60.-k (Nuclear magnetic resonance and relaxation) 78.30.-j (Infrared and Raman spectra)