Niobium-germanium superconducting tapes for high-field magnet applications. Final report, 19 apr. 1976 - 19 nov. 1977. [Nb/sub 3/ Ge]

A process of fabricating superconducting Nb/sup 3/Ge tapes by chemical vapor deposition (CVD) has been developed, and tapes up to 10 meters lone have been fabricated. The typical properties achieved were as follows: critical temperature T sub c = 20 K, upper critical field H sub c2 = 29 tesla at 4.2 K, and J sub c = 3 to 4 x 10 Am-/sub 2/ at 4.2 K, 18 tesla. The relative depression of T sub c and H sub c2 compared with the best thin-film samples sputtered on sapphire was due to the presence of Nb/sup 5/Ge/sup 3/ second-phase particles used as flux pinning centers and to strains induced by thermal mixmatch with Hastelloy B tape substrates. A peculiar field dependence of flux pinning force that was observed in both CVD and sputtered Nb/sup 3/Ge indicated a premature pin-breaking mechanism or a phase inhomogeneity. Directions of further optimization work were defined.