Amorphous superconducting properties

Manning and Briscoe offer two possible explanations for the difference in superconducting properties between vapour-quenched and liquid-quenched alloys. The first explanation is based on the assumption that the liquid-quenched alloys are microcrystalUne rather than amorphous. The observation of a strongly exothermic heat effect (T ) observed by Buschow in the differential scanning calorimetry experiments does not corroborate this view. The second explanation is based on the assumption of an atomic arrangement in the vapour-quenched alloy, which is much more uniformly disordered than in the liquid-quenched alloy. The rather low transition widths A 7 seem to be in favour of this explanation, although even lower ATq values were found in liquid-quenched La .AUj alloys by Johnson and Tsuei (1976). 

Apart from the amorphous rare earth base materials mentioned above, numerous other amorphous metals and alloys have been studied. Collver and Hammond (1973) made a systematic study of amorphous transition metal films obtained by vapour deposition on cryogenic substrates. The superconducting properties of these amorphous alloys show clear differences with those of crystalline alloys. The 7J, values of the latter vary continuously with valency and give rise to two sharp peaks for electron-to-atom ratios equal to 4.5 and 6.5, respectively (Matthias, 1957). In contrast, the Tq values of the amorphous alloys show a more moderate variation with... 

Carbon, as graphite, has strong electrical conductivity properties. It is an important component in electrodes used in a variety of devices, including flashhght cells (batteries). Amorphous carbon has some superconduction capabilities. 

The atomic disorder associated with the amorphous state leads to completely different transport properties from those encountered in the crystalline state. Experimental results of the electrical resistivity, the Hall effect, magnetoresistance, thermoelectric power and the occurrence of. superconductivity are discussed in section 8. The main emphasis is placed on the electrical resistivity. The occurrence of negative temperature coefficients of the resistivity is related to models based on the extended Ziman theory. In the low temperature regime the resistivity often shows a In T... 

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