Superconducting Properties of Laves Phase Compounds in the V-Hf-Zr Ternary System

Abstract

Superconducting transition temperature Tc, upper critical field Hc2 and low temperature specific heat have been measured for Laves phase compounds, V2HfxZr1−x in the V-Hf-Zr ternary system. In this alloy system, the highest Hc2(4.2 K) of 240 kOe and the highest Tc of 10.1 K are achieved for the composition of V2Hf0.55Zr0.45 and V2.3Hf0.5Zr0.5, respectively. Hc2(4.2 K) of this material is higher than that of commercially available high-field superconductor, e.g., Nb3Sn and V3Ga. In addition, this material has a relatively small Vickers hardness, from 280 to 470 depending on x, and is not so mechanically brittle as other high-field superconducting compounds.Electronic specific heat coefficient γ for V2Hf and V2Hf0.5Zr0.5 are 21.7 and 28.3 mJ/atg·K2, respectively. The large γ and spin-orbit scattering effect due to heavy hafnium atoms seem to enhance Hc2 in this material. Debye temperature θD for V2Hf and V2Hf0.5Zr0.5 are 187 K and 197 K, respectively. These low θD might cause relatively low Tc in this material, withstanding the large electron-phonon coupling. The crystal structure of V2HfxZr1−x transforms from cubic to orthorombic at a temperature Tt, ranging from 90 to 160 K. In V2HfxZr1−x, the lower Tt, the higher becomes Tc; the lattice softening associated with the lattice transformation seems to be related with the enhancement of Tc.