J-B-T-ε interaction and strain limits in A15, B1, and C15 crystal structure superconductors

Experimental evidence is presented which indicates, that the elastic strain effect on the critical current of high-field compound superconductors correlates strongly with the type of superconductor crystal structure. Large strain effects are observed in all practical A15 superconductors examined to date, including Nb3Sn, Nb-Hf/Sn-Ga, Nb3Ge, Nb3Al, and V3Ga. Strain is observed to have no measurable effect, however, on either the critical current or the critical field of superconductors having the B1 crystal structure [NbN] or the C15 crystal structure [V2(Hf, Zr)]. Strain limits placed on the mechanical design of superconducting devices are evaluated as a function of magnetic field for several A15 superconductors (Nb3Sn, Nb-Hf/Cu-Sn-Ga, and V3Ga) and compared with the strain limits imposed by B1 and C15 superconductors. It is shown that the latter materials have mechanical design advantage in applications where the superconductor is subjected to strain in excess of 0.2% (either compressive or tensile).