An-Najah Staff

The compositional dependence of the mean atomic volume, V_a, and the packing density, ρ_p, of the Ge_xS_94−xBi₆ glassy system, in the range 14≤x≤26 (x in at.%), have been investigated. Particular features in the compositional dependence of these physicochemical properties on the bond density, n, have been found. Specifically, at n=2.46, V_a and ρ_p exhibit a minimum and a maximum, respectively, whereas at n=2.56, V_a displays a maximum and ρ_p passes through a minimum. These features are explained using the topological arguments proposed in Phillips'–Thorpe and Tanaka's models

The characteristic temperatures such as the glass transition temperature (T_g), the onset temperature of crystallization (T_c) and the melting temperatures, (T_m) have been determined for glasses belonging to the Ge_xSe_{100 − x − y}Fe_y (y = 2, 4 and 6 at.%). Differential scanning calorimetry and differential thermal analysis measurements have been used for their determination. These temperatures have been used to evaluate the thermal stability of the investigated glassy alloys using Dietzel (ΔT) and Hruby (H_r) criteria. The variations of ΔT and H_r with the average coordination number, n, have been specified. It is found that both ΔT and H_r exhibit a maximum at n = 2.4. This observation is a realization of Phillips'–Thorpe threshold where the maximum stability of the network is just obtained if the percolation threshold limit is reached. The overall mean bond energies of the studied compositions have also been calculated and their correlation with the glass transition temperature is discussed.

The compactness of the structure of glassyGexBi6S94-x (14 ≤ x ≤ 26 at %) is determined from the measured densities. The peculiarities observed in the compactness-composition dependence are understood using Phillips’-Thorpe and Tanaka’s topological models proposed for the structure of these covalently bonded solids.