NMR study of Q-speciation and connectivity in K2O–SiO2 glasses with high silica content

The structure of binary potassium silicate glasses with SiO2 content ranging between 76.0 and 97.6 mol% has been studied with 29Si and 17O NMR spectroscopy. Besides the Q3 species, two broadly different types of Q4 species have been identified in the 29Si MAS NMR spectra of glasses with >83.5 mol% SiO2. These species correspond to Q4 connected to one or more Q3 nearest neighbors and Q4 with only Q4 nearest neighbors, and are denoted as Q4–3 and Q4–4, respectively. The compositional variation of the concentration of Q4–3 species implies a statistically random distribution of Q3 and Q4 species in these glasses. Such a silicate network with random connectivity between Q3 and Q4 species is shown to be consistent with the strongly non-linear compositional variation of the transport properties of binary alkali silicate glasses with high silica content.