NOVEL OPPORTUNITIES FOR STUDYING THE SHORT AND MEDIUM-RANGE ORDER OF GLASSES BY MAS NMR, SI-29 DOUBLE-QUANTUM NMR AND IR SPECTROSCOPIES

The glass structure in two ternary systems was investigated with respe ct to their applicability as electrode glasses. For Na2O-Al2O3-SiO2 gl asses, a good pNa electrode signal is observed if (i) AlO4- units exis t, linked mainly to Q(m)(4) units (Q(m)(n): silicate tetrahedra, n: nu mber of Si-O-Si bridges, m: number of Si-O-Al bridges), (ii) some othe r AlO4- units are bonded to mainly Q(m)(3) units and (iii) the conditi on 2 > Q(m)(4)/Q(m)(3) > 1 holds. In Na2O-B2O3-SiO2 glasses, a pNa sig nal 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 reso nance (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 abl e, 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) 19 98 Elsevier Science B.V. All rights reserved.