Inhomogeneous distribution of Na⁺ in alkali silicate glasses

Abstract

We investigated the Na⁺ environment in sodium silicate glasses and mixed alkali silicate glasses using ²³Na multiple-quantum magic-angle spinning (MQMAS) NMR spectroscopy, ab initio molecular orbital (MO) calculations, and Na⁺ elution analysis. The ²³Na MQMAS NMR spectra of Na₂O–xSiO₂ and (1 − y)Na₂O–yM₂O–2SiO₂ (M = Li, K) glasses showed an inhomogeneous distribution of local structures around Na⁺, even though spectral deconvolution was impossible. The quantum chemical calculations indicated that the alkali silicate glasses contained both aggregated and isolated Na⁺ sites. The elution behavior also supported the local structure distribution described above. These results indicated that a cation with a high cation field strength tends to aggregate in mixed silicate glasses.