The superconductivity and metallurgy of C15 materials: Hf-V and Zr-V

Abstract

Variation of theT _c as a function of composition for the C15 materials of the systems Hf−V and Zr−V was investigated. Samples in the as cast and annealed conditions were examined by x-ray and optical metallography. None of the samples was found to be of single phase. For the Hf−V system,T _c increases to a constant value of about 9 K for the compositions between 36 and 60 at. %V. A slight increase ofT _c between 60 and 70 at. %V and a degradation inT _c above 80 at. %V were observed. As cast materials show the maximumT _c value of 9.4 K. Deviations from stoichiometry and heat treatments produce considerable changes in the microstructures but have little effect onT _c . A slight enhancement ofT _c for the alloy containing 80 at. %V is explained by the pressure on V₂Hf due to V phase by the differential thermal contraction. For the Zr−V system, maximumT _c value of 8–6 K was observed for alloys having 20–66 at. %V in as cast condition. Heat treatments cause the lowering ofT _c . Results indicate that the preparation of ZrV₂ superconducting material will need more careful control than would be necessary for HfV₂.