Novel opportunities for studying the short and medium range order of glasses by MAS NMR, 29Si double quantum NMR and IR spectroscopies

The glass structure in two ternary systems was investigated with respect to their applicability as electrode glasses. For Na2O-Al2O3-SiO2 glasses, a good pNa electrode signal is observed if (i) AlO4- units exist, linked mainly to Q(m)(4) units (Q(m)(n): silicate tetrahedra, n: number of Si-O-Si bridges, m: number of Si-O-Al bridges), (ii) some other AlO4- units are bonded to mainly Q(m)(3) units and (iii) the condition 2 > Q(m)(4)/Q(m)(3) > 1 holds. In Na2O-B2O3-SiO2 glasses, a pNa signal is measured if the ratio of the BO4- units linked to BO3 or to Q(4) is less than 1. Two-dimensional double quantum nuclear magnetic resonance (DQ NMR) spectroscopy has been applied to Si-29 enriched sodium silicate glasses for measuring the connectivities of the Q(n) units (m = 0), enabling improved studies of the medium range order. We are able, for the first time, to distinguish between the various Q(3) and Q(4) units bonded to different numbers of Q(3) and/or Q(4) groups. (C) 1998 Elsevier Science B.V. All rights reserved.