Influence of modifier cations on the local environment of aluminum in La2O3–Al2O3 and Y2O3–Al2O3 binary glasses

Abstract

The local environment of aluminum in xLa₂O₃–(100 − x)Al₂O₃ (LA) and yY₂O₃–(100 − y)Al₂O₃ (YA) glasses is investigated using ²⁷Al MAS NMR and Raman scattering spectroscopy in the glass forming range, i.e., 27 ≤ x ≤ 50 and 26 ≤ y ≤ 37.5, respectively. The results suggest that four-fold Al (^[4]Al) is predominant in both glasses, with a content of approximately 90% in LA glasses and 60% in YA glasses; the remaining percentages are made up of five- (^[5]Al) and six-fold (^[6]Al) Al. In LA glasses, the fraction of ^[4]Al increases slightly with an increase in the La₂O₃ content, whereas, in YA glasses, the distribution of Al species does not change. Raman scattering spectroscopy reveals that, in LA glasses, the amount of non-bridging oxygen increases with an increase in x; moreover, ^[5]Al and ^[6]Al both increase with a decrease in x for x ≤ 40. Comparing with alkali earth aluminate glasses, we discuss the relationship between the fundamental structure of the AlO₄ network and two parameters (the ratio of the number of oxygen atoms to that of Al and field strength).