Structural and Magnetic Properties of V-Ti-Si Alloy Superconductors

The structural and magnetic properties of the as-cast and annealed V_0.6-xSi_xTi_0.4 (x = 0, 0.05, 0.10, 0.15) alloy superconductors are reported here. It is found that addition of silicon to the V-Ti alloys results in eutectic precipitation of Ti_5Si_3-phase in the body centred cubic (bcc) β-V-Ti matrix. In the as-cast V_0.6-xSi_xTi_0.4 alloys, the superconducting transition temperature (T_C) changes non-monotonically with increasing silicon content whereas after annealing, it is about 7.7 K for all the alloys. On the other hand, the upper critical field decreases and the coherence length increases after annealing in the x = 0.10 alloy. The variations in the superconducting properties in the alloys are related to the solubility of 6 at. the vanadium enrichment in the β matrix due to the precipitation of Ti_5Si_3 phase.