Bulk glasses with the chemical composition Gey Se94−yIn6 (8 ⩽ y ⩽ 30
at%) have been prepared from high purity constituent elements.
Fragments of the bulk glasses are used to deposit thin films by vacuum
thermal evaporation. The optical band gaps (Eg s) of the as-deposited films have been measured. The allowed optical transition is found to be indirect. The relation of Eg to the covalent coordination number, Z, is demonstrated by varying the composition parameter y of the thin films. A maximum in the compositional dependence of Eg is attained at Z = 2.63.
The cohesive energies (CE) of the investigated samples have also been
calculated using the method suggested by the chemical bond approach. It
is found that the composition dependence of the CE also possesses a peak
at Z = 2.63.A plausible explanation based on the
bonding considerations between the constituents has been provided for
the understanding of the Eg-Z and CE-Z dependences for these Ge–Se–In thin films.