The percentages of B 4 atoms are plotted with blue lines in Fig. (left-hand axes) as a function of temperature. The trends of their percentage changes from 1500 to 300 K are indicated by the dotted lines in Fig. . For the a-La30 and a-La50 systems, the cooling process leads to a weak increase in B 4 ; conversely, the percentage of B does not make a dominant contribution, and the change in the B 4 percentages for the melt and solid glass are as small as ∼3%. Interestingly, the change in the B 4 percentage during the cooling process for a-Y50 glass was as high as ∼7%; this suggests that Y 3+ has a similar role to that of Na + in the melt. In other words, this behavior is associated with the higher ionicity of Y 3+ compared to La 3+ , similar to Na + .