Structural and magnetic properties of the as-cast V1−xZrx alloy superconductors

Abstract

We report here the structural, electrical, thermal, and magnetic properties of the as-cast V1−xZrx alloys (x=0–0.4) at low temperatures. We observe that all the alloys undergo successive peritectic and eutectic reactions during cooling from the melt, which leads to the formation of five phases, namely, a body centered cubic β-V phase, two phases with slightly different compositions having a face centered cubic ZrV2 structure, a hexagonal closed packed α-Zr phase, and the β-Zr precipitates. The amount of each phase is found to be dependent on the concentration of zirconium in vanadium. The β-V and ZrV2 phases show superconductivity below 5.2 K and 8.5 K, respectively. We show that the critical current density is large for the V-rich V1−xZrx alloys with x>0.1. The grain boundaries generated from the eutectic reaction and the point defects formed due to the variation in the composition are found to be responsible for the pinning of flux lines in low and high magnetic fields, respectively. Our studies reveal that the choice of the composition and the heat treatment, which leads to eutectic reactions are important in improving the critical current density in this alloy system.