Broken chemical order in Ge-Sb-Se glasses for use as infrared-transmitting lenses

Raman spectroscopic analysis was employed in an effort to refine the structure-property relation of Ge-Sb-Se glasses mainly in a Ge-rich compositional range appropriate for use in molded infrared-transmitting lens applications. Based on our Raman analysis, it was reconfirmed that each constituent atom satisfies the '8 − N' rule. However, it was newly verified that the chemical preference favoring heteropolar bonds to Se atoms is violated, thus unveiling the existence of nontrivial amount of homopolar bonds between Ge and Sb atoms even in the Se-rich compositions. Thermal and mechanical properties of the glasses tended to improve with increase of these homopolar bonds. As such, presence of the homopolar bonds between Ge and Sb atoms, more abundant than expected from the stoichiometric ratios, implies that this broken chemical order per se exerts a positive influence as to the infrared optics applications.