Oxygen-17 Nuclear Magnetic Resonance Study of the Structure of Mixed Cation Calcium−Sodium Silicate Glasses at High Pressure: Implications for Molecular Link to Element Partitioning between Silicate Liquids and Crystals

Abstract

The structure of silicate glasses and the corresponding liquids at high pressure and their structure-property relations remain difficult questions in modern physical chemistry, geochemistry, and condensed matter physics. Here we report high- resolution solid-state O-17 3QMAS NMR spectra for mixed cation Ca-Na silicate glasses quenched from melts at high pressure up to 8 GPa. The spectra provide the experimental evidence for the varying pressure-dependence in two different types of nonbridging oxygen (NBO) environments (i.e., Na-O-Si and mixed (Ca,Na)-O-Si) in the single glass composition. The percentage of NBO drops significantly with increasing pressure and is a complex function of melt composition, including cation field strength of network modifying cations. A decrease in NBO fraction with pressure is negatively correlated with the element partitioning coefficient between crystals and liquids at high pressure.