Thermal expansion behavior of Ge-Sb-Se glasses in a compositional range for molded infrared lens applications.

The thermal expansion coefficient ( TEC) of Ge-Sb-Se glass, within a compositional range suitable for molded lenses capable of transmitting long-wavelength infrared, was analyzed to assess compositional dependence. Unlike other thermal properties, eg, glass transition temperature and dilatometric softening temperature, which are correlated mostly with germanium content, the TEC turned out to behave most sensitively with selenium content. The thermal expansion behavior 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 mean 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 behavior of this glass is delineated, with a particular focus on its connection to the structural role of the Se atoms. [ABSTRACT FROM AUTHOR]