The thermal expansion coefficient (TEC) of Ge-Sb-Se glass, within a compositional range suitable for moulded lenses capable of transmitting long-wavelength infrared, was analyzed to assess compositional dependence. Unlike other thermal properties, e.g. glass transition temperature and dilatometric softening temperature, behave most sensitively with selenium content. The thermal expansion behaviour of this glass was evaluated based on two structural parameters: the mean coordination number and average bond energy (ABE). It was verified that the relation between TEC and these structural parameters needs to be distinguished in terms of homopolar Se-Se bonds. Specifically, the TEC tends to decrease monotonically as the man coordination number increases, and there are relatively small discrepancies between Se-sufficient and Se-deficient compositions. The TEC of the Se-sufficient glass appears to have a relatively well-defined correlation with the ABE: the TEC decreases as the ABE increases. However, a much weaker correlation between the TEC and ABE is observed in the Se-deficient glass. The observed thermal expansion behaviour of this glass is delineated, with a particular forus on its connection to the structural role of the Se atoms. .
