Effect of strain on the critical current of Nb3Ge

The strain dependence of the critical-current density has been determined for composite tapes of Nb3Ge prepared by chemical vapor deposition. For Nb3Ge layers 3-4 μm thick deposited on a nickel-molybdenum-iron alloy substrate, the critical current monotonically increases when uniaxially strained to about 0.6%. This strain corresponds almost exactly to the compressive strain that would be introduced into the Nb3Ge by the substrate due to thermal contraction during cooldown after reaction. The increase in critical current was relatively small, about 6½% at 7T and 5½% at 4T. At higher strain, the critical current decreased rapidly, falling by more than 50% at a strain of 0.9%, for example. For Nb3Ge deposited on a tantalum substrate, however, the critical current monotonically decreased, falling by more than 50% at a strain of 0.4%. The results indicate that Nb3Ge can withstand considerable compressive strain (at least 0.6%), but fractures at tensile strains of only 0.1 to 0.2%.