Novel opportunities of structural investigations of glasses by 2D NMR, multiple quantum NMR and 27Al MAS NMR lineshape analysis

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Abstract
The recent progress in NMR of glasses is demonstrated using both traditional and improved two‐dimensional (2D) NMR techniques. A novel approach for measuring connectivities Qn units in amorphous and polycrystalline solids is explained. Several examples of phosphate samples are presented to show e.g. how chain end groups can be distinguished from pyrophosphate units. Additionally, novel results of 27Al NMR investigations in mullites and Na2O‐SiO2‐Al2O3 glasses were obtained using a careful lineshape analysis. In mullites three different AlO4 units can be found including an estimation of the relative Al occupancy of the various groups. In ternary Na2O‐Al2O3‐SiO2 glasses we could prove the presence of two AlO4 sites with Al being surrounded by four Q3 units or possibly one terminal oxygen instead of a Q3 unit (60 ppm) and by four Q4 groups (53 ppm). Finally, two different Na sites have been detected for the first time using 23Na MQ NMR in a glass 22.7 Na2O 0.7 B2O 69.8 SiO2.