Some comments on physical properties of chalcogenide glasses

This paper is a brief review of our previously published results in addition to a recent study of the microhardness of chalcogenide glasses measured as a function of the average covalent coordination number, 〈r〉. Glasses in the pseudoternary system Ge–(Sb·As)–(Se·Te) were prepared by vacuum melting of previously distilled 5N to 6N pure raw materials. Several physical properties, namely, density (molar volume), elastic moduli, static and dynamic microhardness, indentation toughness, thermal expansion coefficient, glass transition temperature, viscosity, and acoustic attenuation have been measured and published previously. Most glassy state properties have a monotonic relation with 〈r〉. Molar volume and the configurational contribution (difference between liquid state and glassy state properties) to second derivative thermodynamic properties, on the other hand, have minima at the rigidity percolation threshold 〈r〉=2.40. Newly obtained microhardness data using a recording indenter show that binary chalcogenide glasses have a dynamic Vickers microhardness, called `DVHʹ achieving a maximum at 〈r〉=2.4. Whereas the energy required for plastic and unrecovered elastic deformations is largest for Se (〈r〉=2.0 glass), the elastic energy recovery upon unloading the indenter appears to be a maximum at 〈r〉=2.4. Based on these observations I suggest that the 〈r〉=2.4 structure has the largest yield strength and, in turn, is the most connected network among the binary glasses.