Microstructure and superconductivity of some C15 laves phase alloys: V2Hf, V2Hf.51Nb.49and V2Hf.51Nb.21Ti.28

Effect of different heat treatments on the lattice structure, microstructure and superconductivity of the C15 phase materials: V2Hf, V2Hf.51Nb.49and V2Hf.51Nb.21Ti.28are investigated. X-ray, optical microscopy and SEM investigations show the distribution of C15 phase filaments (10-25μ) in a bcc matrix for the V2Hf.51Nb.49and V2Hf.51Nb.21Ti.28materials. The composition of the filaments is sensitive to heat treatment and the maximum ratio of V to Hf, Nb and Ti atoms is obtained after annealing the V2Hf.51Nb.21Ti.28at (1200°C;6h). Tcincreases and the Vicker\´s hardness decreases after the substition of Nb and Ti for the Hf in V2Hf compound. Maximum Tcand Hc2(8K) values of 9.76K and 9.4 Tesla are also observed for the annealed (1200°C;6h) V2Hf.51Nb.21Ti.28alloy. Anomalies in (R vs. T) and ( vs. T) curves are observed for the homogeneous V2Hf (annealed 900°C;70h) at ∼ 130K and 150K respectively, whereas multifilamentary annealed (900°C;70h) V2Hf.51Nb.49and V2Hf.51Nb.21Ti.28do not show such anomalies. Tcvalues of annealed (900°C;70h) V2Hf, V2Hf.51Nb.49and V2Hf.51Nb.21Ti.28are 8.89K, 9.07 and 9.71K respectively. It is concluded that for these alloys the lattice instability is microstructure dependent and does not influence the superconducting parameters.