Influence of modifier cations on the local environment of aluminum in LaO-AlO and YO-AlO binary glasses.

The local environment of aluminum in xLaO-(100 -x)AlO (LA) and yYO-(100 -y)AlO (YA) glasses is investigated using Al 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 (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- (Al) and six-fold (Al) Al. In LA glasses, the fraction of Al increases slightly with an increase in the LaO 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, Al and 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 AlO network and two parameters (the ratio of the number of oxygen atoms to that of Al and field strength).