Journal of M olecular Structure, 247 (1991) 1-16 Elsevier Science Publishers B.V., Amsterdam zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJ Borate glass structure by Raman and infrared spectroscopies* E.I. Kamitsos and G.D. Chryssikos Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48, Vass. Constantinou Ave., Athens 116 35 (Greece) (Received 22 January 1990) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC Abstract Raman and infrared spectroscopies have been employed to probe the continuous evolution of borate glass structures as a function of the nature and concentration of alkali oxide modifier. At relatively low alkali contents, the glasses contain covalent networks consisting of interconnected units bearing BO, tetrahedra. Further addition of alkali oxide causes the progressive depolymer- ization of the network as a result of the formation of non-bridging oxygen atoms. Eventually, complete network disruption into small and highly charged borate units results in “ionic” glasses. The nature of the alkali cation determines the structure of these glasses by affecting several high- temperature isomerization or disproportionation equilibria. INTRODUCTION Binary alkali borate glasses xMzO (1 -x)B,O, (M, alkali metal) have been extensively studied over the years to elucidate the nature and the relative con- centration of the various borate units constituting the glass network. The ul- timate goal has been to understand the structural peculiarities of these mate- rials, which are manifested in the non-monotonic variation of most physical properties with x and are widely known as the “boron anomaly effect” [ zyxwvutsrqponmlkjih 11. The NMR investigation of Bray and co-workers [2,3] as well as the vibrational work of Krogh-Moe [ 41 and Konijnendijk and Stevels [ 51 have been particu- larly helpful in identifying various boron-oxygen arrangements at different modification levels. These studies have put emphasis on the effect of modifier content (x) on the glass structure, but have provided little or no insight into the possible dependence of the latter on the nature of the particular alkali employed. Interest in structural studies of borate glasses has been renewed since the discovery of glass compositions with exceptionally high ionic conductivity, *Dedicated to the memory of Professor George Wilkinson. 0022-2860/91/$03,50 0 1991- Elsevier Science Publishers B.V.