Synthesis and physical properties of chalcogenide glasses in the system BaSe–Ga2Se3–GeSe2

• Chalcogenide glasses are synthesized in the system BaSe–Ga2Se3–GeSe2.
• Compositional variation of optical band gap, density, Tg and fragility are reported.
• Structure–property relationships are explored.
• Compositions with 2Ba/Ga = 1 act as a chemical threshold
• Structural roles of Ba and Ga as modifier and intermediate are explored.

Chalcogenide glasses in the system BaSe–Ga2Se3–GeSe2 have been synthesized and their optical band gap, density, glass transition temperature and fragility have been measured. The band gap and density exhibit nearly linear variation with Ba:Ga ratio at a fixed GeSe2 content. On the other hand, the glass transition temperature and fragility display either a clear maximum or a break in slope near 2Ba/Ga = 1. The compositional dependence of these physical properties are consistent with a scenario where the atomic structure of these glasses transforms across 2Ba/Ga = 1 that behaves as a chemical threshold between a Se-poor network with Ge/Ga–Ge/Ga bonding and a network characterized by Se–Se bonding and/or the formation of non-bridging Se atoms.