Kinetics of structure relaxation

The hydrogen diffusion coefficient is not constant, but decreases with time (Street et al. 1987b). The data in Fig. 2.22 show a power law decrease in p-type a-Si H of the form r , with a 0.2 at the measurement temperature of 2(X) C. The time dependence is associated with a distribution of traps originating from the disorder. A similar effect is found in the trap-limited motion of electrons and holes and is analyzed in Section 3.2.1. The time dependence of is reflected in the kinetics of structural relaxation discussed in Section 6.3.1. 

Taub, A. J. and Spaepen, F. (1980) The kinetics of structural relaxation of a metallic glass, Acta MetalL, 28, 1781-1788. 

In addition to the free volume [36,37] and coupling [43] models, the Gibbs-Adams-DiMarzo [39-42], (GAD), entropy model and the Tool-Narayanaswamy-Moynihan [44—47], (TNM), model are used to analyze the history and time-dependent phenomena displayed by glassy supercooled liquids. Havlicek, Ilavsky, and Hrouz have successfully applied the GAD model to fit the concentration dependence of the viscoelastic response of amorphous polymers and the normal depression of Tg by dilution [100]. They have also used the model to describe the compositional variation of the viscoelastic shift factors and Tg of random Copolymers [101]. With Vojta they have calculated the model molecular parameters for 15 different polymers [102]. They furthermore fitted the effect of pressure on kinetic processes with this thermodynamic model [103]. Scherer has also applied the GAD model to the kinetics of structural relaxation of glasses [104], The GAD model is based on the decrease of the crHiformational entropy of polymeric chains with a decrease in temperature. How or why it applies to nonpolymeric systems remains a question. 

The kinetic character of the glass transition and the resulting non-equilibrium character of the glassy state are responsible for the phenomena of structural relaxation, glass transition hysteresis, and physical aging (Kovacs, 1963 Struik, 1978). 

With a simple change of notation the present theory may be used to set the Gilroy and Philips model [82] of structural relaxation processes in amorphous materials and Dyre and Olsen s minimal model for beta relaxation in viscous liquids [83] in the framework of the general theory of stochastic processes. Moreover, the formulation of the theory in terms of kinetic equations as the... 

In addition to controlling the magnitude of structural relaxation, fragility also affects the kinetics of the relaxation process. This is easily seen by inspection of the Tool-Narayanaswamy-Moynihan (TNM) equation [53] ... 

The kinetic features of structural relaxation in polymer glasses were first reported by Kovacs in the 1960s [70]. He systematically studied the structural relaxation phenomenon by measuring the volumetric response of polymers subjected to various thermal histories. The findings can be summarized as three ingredients [71] (1) intrinsic isotherm, (2) asymmetry of approaching equilibrium, and (3) memory effect. 

Concurrently with experimental investigations, structural relaxation has also received a great deal of interest from theoretical studies. Several kinetic or thermodynamic models were developed to capture the three essential ingredients of structural relaxation. Among these models, the most famous two are the Tool-Narayanaswamy-Moynihan (TNM) model [96-98] and the Kovacs-Aklonis-Hutchinson-Ramos (KAHR) model [99]. 

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