Correlation between basicity and coordination structure in borosilicate glasses

Various quaternary borosilicate glasses in the general system M ₂O-M'O-Al₂O₃-B₂O₃- SiO₂ (M=Li, Naor K; M'=Ca, Sr or Ba) were prepared, and the concentration of four-fold coordinated boron (B4) atoms was determined using¹¹B magic angle spinning NMR. Regression analyses were performed to predict the B4 fraction, in which B4 fraction and glass basicity were used as dependent and independent variables, respectively. Except for Al ₂O₃-containing glasses, regression formulae giving high correlation coefficients were successfully obtained by using B4/(B+Si×f) (where f is a tunable coefficient) as the dependent variable. As for the glasses containing Al₂O₃, however, the necessity of a different dependent variable was indicated.