Nagel-Tauc criterion

Fig. 5.29. Structure data of Fe-Sb metallic glasses 5.22]. Pure Sb is taken from [5.50], a) Structure factor b) pair-distribution function. Vertical lines in both figures indicate 2kF or rj, respectively. ZFe = 1 e/a was used for their calculation c) ion (local moment) positions vs. composition, compared with the position of minima in eff(r) and maxima of Jaf(r) calculated with ZFe = 1.0-1.1 e/a (thin solid curves). The thin dashed curve indicates a favourable antiferromagnetic position of local moments. The thin vertical lines in c) indicate approximately the composition where the Nagel-Tauc criterion is best fulfiled... 

From these results it can be concluded that any favourable (2kp= Q ) or unfavourable (2kp Q ) influence on E, even if it were of the order of AH, would have little effect on the magnitude of AE. This means that the Nagel and Tauc criterion is less suited for describing thermal stability of amorphous alloys, i.e. their resistance against crystallization. As briefly indicated above, it is mainly the transformation kinetics that governs the thermal stability of amorphous alloys. A description of the kinetic approach to thermal stability will be presented in the following section. 

The particular position taken by alloys for which 2kp = was already mentioned in connection with the Nagel and Tauc criterion discussed in sections 3.1 and 4.2. In the latter section we showed that the Nagel and Tauc criterion is less suited for describing the thermal stability of amorphous alloys. In the former section the possibility was discussed that amorphous alloys for which the criterion 2kp is satisfied may be amenable to easy glass formation owing to the presence of an enhancement of the deepness of the eutectic. 

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