Heat treatment effect on thermal, superconducting and structural properties of amorphous sputtered Zr76Cu24alloy

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Abstract
The authors report and discuss measurements of low-temperature specific heat and thermal conductivity, upper critical field near Tc, electrical resistivity, mass density and X-ray diffraction, performed on an amorphous superconducting Zr76Cu24 alloy obtained by high-rate sputtering deposition at 77K. A thermal annealing of the samples in the amorphous state before crystallisation induces a large decrease of the very low-temperature specific heat related to the two-level system excitations, whereas the thermal conductivity increases in a correlative way. Both electron and phonon contributions to the specific heat in the normal state decrease and tend towards the values of liquid-quenched (LQ) alloys of corresponding composition. At the same time, the other properties studied are less affected, likewise in LQ alloys. The occurrence upon annealing of a chemical phase separation in the amorphous state is proposed to explain the results.