Structure and physical properties of Ge_x As_y Se _1-x-y glasses with the same mean coordination number of 2.5

We have prepared and analyzed five different compositions of Ge_x As_y Se_1-x-y glasses that have the same mean coordination number (MCN) of 2.5 in order to understand whether MCN or chemical composition has the dominant effect on the physical properties of the glass. Density measurements showed a maximum for the chemically stoichiometric Ge12.5 As25 Se62.5 sample and suggested that some rearrangement of the atoms was occurring as one atom substituted for another. The measurements of T_g, however, showed that the glasses had almost same glass transition temperature and suggested that the glass network connectivity did not change much with composition. Although Raman scattering and x-ray photoelectron spectra of the glasses indicate that the percentage of the different structural units changes with the composition, there was no evidence of the existence of structural units that could change the overall connectivity of the glass network. Therefore, we concluded that glasses with same MCN but different composition have similar glass network connectivity, and that chemical composition has only a secondary effect on the physical properties of the glasses.