Application of the Free Volume Concept to Glasses in the Ge–As–S System

The energy of hole formation E _h, the hole volume V _h, and the fraction f _g of fluctuation free volume for glasses in the Ge–As–S system are calculated from the data on the elastic moduli, the microhardness H, and the glass transition temperature T _g. It is shown that the fraction of fluctuation free volume in ternary glasses is considerably larger than that in arsenic chalcogenide glasses. For the glasses studied, the E _h energies fall in the range 13–18 kJ/mol and the hole volumes are equal to (7–84) × 10^–6 m³/mol. The concentration dependences of the elastic moduli and the parameters of the free volume theory for glasses in the As₂S₃–GeS₂ system are less pronounced than those for glasses in the As–S system with small coordination numbers of glass-former ions. This is explained by the topological transition observed in glasses of this system at a high germanium content. It is demonstrated that the parameters of the fluctuation free volume theory are related to the characteristics of the boson peak in the Raman spectra.