Structural Relaxation in Relation to Fragility and Mean Coordination

5 Structural Relaxation in Relation to Fragility and Mean Coordination 

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 structural rearrangement processes responsible for enthalpy relaxation tend to be very slow at room temperature, where little thermal energy is available to activate molecular reorientations. Equation [2.4] indeed shows that the structural relaxation time increases exponentially with decreasing temperature. Hence these processes are typically hard to observe on a laboratory timescale. However, chalcogenides also possess the unique property of photosensitivity, which offers another means of inducing structural 

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