Local Structure of Magnesium in Silicate Glasses: A 25Mg 3QMAS NMR Study.

We have reported the 25Mg triple-quantum magic-angle spinning (3QMAS) NMR spectra of silicate glasses. The two-dimensional spectra suggest that the magnesium ions in MgSiO 3, CaMgSi 2O 6, Ca 2MgSi 2O 7, Mg 3Al 2Si 3O 12, and Li 2MgSi 2O 6glasses are mainly in octahedral environments, although in Na 2MgSi 2O 6, K 2MgSi 2O 6, and K 2MgSi 5O 12glasses they form tetrahedral species. We discussed the coordination environments of Mg based on the field strength of competing Mg 2+, Ca 2+, Na +, K +, and Li +cations, and convincingly demonstrated that there is a correlation between them. These results indicate that the two-dimensional NMR spectroscopy such as MQMAS technique is a very useful method to analyze the local environments of nonframework cations in noncrystalline solids. [ABSTRACT FROM AUTHOR]