Structural characterization of glass from the inversion of Na-23 and Al-273Q-MAS NMR spectra

A spectrum-inversion approach to extract information from MQ-MAS NMR spectr a in glasses is presented. This allows the reconstruction of the underlying two-dimensional distribution of the isotropic chemical shift correlated to the quadrupolar interaction. The dependency upon the quadrupolar interacti on and the RF field strength of coherence transfers involved in the MQ-MAS experiment are taken into account in the present approach. The performance of the inversion procedure is examined. Thereafter, we attempt to correlate the distributions of each interaction to structural local information. Two complex glasses (a borosilicate and a basaltic-like glass) have been studi ed using Al-17 and Na-23 3Q-MAS NMR. These two nuclei allowed us to investi gate their local environment. The interpretation of the different site dist ributions is discussed in terms of topological disorder, i.e., the distribu tion of specific geometrical parameters such as bond distances and angles. Using the semiempirical relationships previously established with crystalli ne silicate compounds, the distributions of the Na-O distance and the Al-O- Si bond angle have been determined from the extracted distributions of the isotropic chemical shift. The limits of the interpretation of quadrupolar i nteraction distributions are also discussed.