Structural investigation of Mg local environments in silicate glasses by ultra-high field ²⁵Mg 3QMAS NMR spectroscopy

Structural information on divalent cations such as Mg²⁺ should have important implications for magmatic liquids because of their abundance in the Earth’s interior; nevertheless, little is confirmed about their coordination environments. We here apply a ²⁵Mg triple-quantum magic-angle spinning (3QMAS) NMR technique at an ultra-high magnetic field (21.8 T) and successfully show the occurrence of multiple Mg sites in MgSiO₃ glass. We find that these sites are distinguished by the degree of polyhedral distortion, not by the coordination number. The present study concludes that the highly distorted MgO₆ species occur in MgSiO₃ glass, in strong contrast with a recent radial distribution study.