Superconductivity in V$_{1-x}$Zr$_x$ alloys]{Evolution of high field superconductivity and high critical current density in the as-cast V$_{1-x}$Zr$_x$ alloys

Abstract

We report here the structural, electrical and magnetic properties of as-cast V 1−x Zr x 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 centred cubic β-V phase, two phases with slightly different compositions having face centred cubic ZrV 2 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 ZrV 2 phases show superconductivity below 5.3 K and 8.5 K respectively. We show that the critical current density is large for V-rich V 1−x Zr x 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 reaction are important in improving the critical current density in this alloy system.

Two channel heat conduction in the superconducting state of the as-cast V$_{1-x}$Zr$_x$ alloys

“…The solubility of zirconium in vanadium at room temperature is only about 2% [11]. However, when cooled rapidly, the partial completion of the peritectic reaction results in the eutectic type reaction even in the 0.02≤ x ≤ 0.33 alloys [9]. Therefore, five different structural phases namely β-V, γ-ZrV 2 , γ ′ -ZrV 2 , β-Zr and α-Zr are observed in the present alloys [9].…”

“…However, when cooled rapidly, the partial completion of the peritectic reaction results in the eutectic type reaction even in the 0.02≤ x ≤ 0.33 alloys [9]. Therefore, five different structural phases namely β-V, γ-ZrV 2 , γ ′ -ZrV 2 , β-Zr and α-Zr are observed in the present alloys [9]. Figure 1 shows the high resolution scanning electron microscopy (SEM) images of x = (a) 0.2 and (b) 0.4 alloys.…”

“…The lamellar structure in both these alloys contains γ-ZrV 2 and α-Zr phases. The details of microstructures of the as-cast V 1−x Zr x alloys (non-equilibrium phase diagram) can be found elsewhere [9].…”

“…The buttons were remelted six times to ensure homogeneity. The details of metallography can be found elsewhere [9]. The temperature dependence of resistivity, heat capacity and thermal conductivity were measured in a 9 T Physical Property Measurement System (PPMS, Quantum Design, USA).…”

“…Current interest in these materials stems from the recent developments in the processing technologies such as the powder in tube (PIT) technique, rapid heating and quenching (RHQ) and the rod restack process etc., for fabricating superconducting wires [7,8]. Recently, we have shown that the multicomponent V 1−x Zr x alloy superconductors are potential candidates for high field applications [9].…”