Inhomogeneous distribution of Na+ in alkali silicate glasses

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We investigated the Na[+] environment in sodium silicate glasses and mixed alkali silicate glasses using [23]Na multiple-quantum magic-angle spinning (MQMAS) NMR spectroscopy, ab initio molecular orbital (MO) calculations, and Na[+] elution analysis. The [23]Na MQMAS NMR spectra of Na[2]O–xSiO[2] and (1 − y)Na[2]O–yM[2]O–2SiO[2] (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.