Low-temperature annealing effects upon the superconducting properties of V 3Au

Abstract

The superconducting transition temperature, T 0, and the initial slope of the upper critical magnetic field curve of V 3Au have been measured as functions of low (400°C–800°C) temperature annealing. T 0 ranges from no superconductivity down to 0.015 K to a T 0 as high as 3.22 K. X-ray diffractometer data indicated that all the samples employed in this study had the A15 structure. Metallographic studies indicated the presence of a few percent of a second Au rich phase in these equilibrated samples. The X-ray data also indicated that the low-temperature anneals did change the degree of crystallographic long range order present in the samples and our data clearly indicate that T 0 increases quite markedly as the Bragg-Williams long-range order parameter approaches the value of unity. The magnitude of the initial slope of the critical magnetic field curve also increases with increase in T 0( from -22 × 10 3 Oe/ deg to -37 × 10 3 Oe/ deg for T 0 = 0.89 K and 3.1 K respectively) with one exception, and that is the sample with the highest T 0 for which the slope has its smallest value, namely -16 × 10 3 Oe/ deg.