Structural relaxation in chalcogenide glasses

Abstract

The structural relaxation of chalcogenide glasses is discussed within Tool-Narayanaswamy-Moynihan (TNM) formalism. The TNM parameters for more than 70 different glassy compositions are compared on the basis of the relaxation rate defined as R f (ΔT) = −(dT f /dlogt) i at the inflection point of the isothermal relaxation curve plotted on a logarithmic timescale. The R f (ΔT) depends on the TNM parameter ß and the parameter σ, combining the nonlinearity parameter x, the effective activation energy h* or the fragility m. It is shown that R f (10) estimated at 10 K below T g is useful for the prediction of structural relaxation kinetics in different amorphous materials. The chalcogenide glasses are, for example, compared with oxide glasses and organic polymers. For all these materials, the R f (10) versus σ plot shows a well-defined pattern that is thoroughly discussed.

Structural Relaxation Rate and Aging in Amorphous Solids

“…Solid blue lines were calculated by eq for constant values of the nonexponentiality parameter 0.2 ≤ β ≤ 0.8. The points correspond to the R 10 data calculated by eqs , , and for 250 different sets of TNM and KAHR parameters reported for various types of amorphous materials: polymers, ,− epoxy resins, − sugars, − hydrated starch, , organic molecules, − oxide glasses, ,,− chalcogenide glasses, halide glasses, metallic glasses, , volcanic glasses, , and tektite, as well as for materials described by AGSH parameters. − ,,− …”

“…Solid blue lines were calculated by eq 15 for constant values of the nonexponentiality parameter 0.2 ≤ β ≤ 0.8. The points correspond to the R 10 data calculated by eqs 12, 13, and 15 for 250 different sets of TNM and KAHR parameters reported for various types of amorphous materials: polymers, 24,33−43 epoxy resins, 44−51 sugars, 52−55 hydrated starch, 56,57 organic molecules, 58−60 oxide glasses, 13,23,61−69 chalcogenide glasses, 70 halide glasses, 20 metallic glasses, 71,72 volcanic glasses, 73,74 and tektite, 75 as well as for materials described by AGSH parameters. 23−25,45,76−78 All these data are enclosed within the upper and lower bounds of the nonexponentiality range 0.2 ≤ β ≤ 0.8, with notable exception of some chalcogenide glasses such as: (Ge-Te 4 ) y (GaTe 3 ) 100−y and Ag x [(GeS 2 ) 50 (Sb 2 S 3 ) 50 ] 100−x, 79,80 as well as obsidian volcanic glasses from Tenerife.…”

“…Therefore, for amorphous materials with very 24 selenium glass, Se (β = 0.58, σ = 0.257 K −1 ), 25 and As 2 S 3 glass (β = 0.82, σ = 0.095 K −1 ). 26 Points correspond to experimental data for dilatometric experiments 25−29 70 halide glasses, 20 metallic glasses, 71,72 volcanic glasses, 73,74 tektite, 75 and materials described by AGSH parameters. 23−25,45,76−78 high nonlinearity contribution (PVC, σ ≅ 1.6 K −1 ), the available range of R 10 is ≈0.4 K/decade of time, which is comparable to the margin of the experimental error.…”

“…Comparison of parameter σ m estimated by eq 16 by using viscosity data for chalcogenide melts, 88 viscosity shear compliance, and modulus data for polyvinyl acetate (PVAc), polycarbonate (PC), polymethyl methacrylate (PMMA), and polyvinyl chloride (PVC), 89 and parameter σ calculated by eq 12 using dilatometric and calorimetric structural relaxation data. 70 The relaxation data for some chalcogenide glasses and organic polymers calculated in this way by eq 12 along with estimations σ m obtained by eq 16 for the same materials. It is seen that these estimates based on fragility and T g value agree reasonably well with the calorimetric or dilatometric structural relaxation experiment.…”

“…Relaxation rate at T g −10 as a function of nonlinearity contribution σ. Points correspond to predictions calculated by eqs – for TNM or KAHR parameters reported for various amorphous materials: organic polymers, ,− epoxy resins, − sugars, − starch, , organic molecules, − oxide glasses, ,,− chalcogenide glasses, halide glasses, metallic glasses, , volcanic glasses, , tektite, and materials described by AGSH parameters. − ,,− Solid lines were calculated by eq for constant values of the nonexponentiality parameter β indicated next to the curves. The dashed lines indicate five different ranges of the structural relaxation rate.…”