STRUCTURAL INVESTIGATION OF MG LOCAL ENVIRONMENTS IN SILICATE GLASSES BY ULTRA-HIGH FIELD 25MG 3QMAS NMR SPECTROSCOPY

Abstract

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.