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

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).