Physical properties of barium borate glasses determined over a wide range of compositions

Barium borate glasses are reported over an extended glass-forming range from R=0.2 (16.7 mol% BaO) to R=2.0 (66.7 mol% BaO), where R is the molar ratio of barium oxide to boron oxide. The density, Tg (glass transition temperature), Tx (glass recrystallization temperature), and optical cutoffs were determined. These data were compared with structural models for the glasses based on nuclear magnetic resonance results of Greenblatt and Bray. The barium borate data were also compared with similar studies of lithium and lead borate glasses. Key results observed include: (1) the density trends are understandable in terms of the abundance of the basic borate groups with the fraction of tetrahedral borons being the most important single factor, and (2) the Tgs are anomalously high when compared to either the alkali or lead borate systems.