Structure of Rubidium Borosilicate Glasses Studied by Nuclear Magnetic Resonance Spectroscopy

Abstract

We present results of an ¹¹B and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy study of the local anion structure of a series of borosilicate glasses in the Rb₂O–B₂O₃–SiO₂ system with different R = [Rb₂O]/[B₂O₃] and K = [SiO₂]/[B₂O₃] molar ratios. Relative integrated intensities of NMR lines are used to evaluate the fractions of boron atoms in three- and fourfold coordinations and the concentrations of various types of Qⁿ silicate units. Comparison of the present data on the anion structure of the Rb₂O–B₂O₃–SiO₂ glasses studied here and data for previously studied glasses of analogous compositions in the Cs₂O–B₂O₃–SiO₂ system demonstrates that the difference in the degree of depolymerization in the anion structure of the glasses in these two systems is most pronounced at R = 1 and K = 2. At other values of these composition parameters (R = 0.43 and K = 1.43 or R = 2.33 and K = 3.33), the glasses with the compositions studied in the Rb₂O–B₂O₃–SiO₂ and Cs₂O–B₂O₃–SiO₂ systems are rather similar in local anion structure. The observed structural distinctions between the glasses make it possible to find out why they differ in glass transition temperature, as shown in a previous study by differential scanning calorimetry.