Reversible axial-strain effect in Y–Ba–Cu–O coated conductors**Contribution of NIST, an agency of the US Government, not subject to copyright.

Abstract

The recently discovered reversible strain effect in Y–Ba–Cu–O (YBCO) coated conductorscontrasts with the general understanding that the effect of strain on the critical-current densityJc in practical high-temperature superconductors is determined only bycrack formation in the ceramic component. Instead of having a constantJc as a function of strain before an irreversible drop when cracks form in the superconductor,Jc in YBCO coated conductors can decrease or increase reversibly with strain over asignificant strain range up to an irreversible strain limit. This reversible effect is present insamples fabricated either with rolling-assisted biaxially textured Ni–W substrates orwith ion-beam-assisted deposition on Hastalloy substrates. The reversibility ofJc with strain is observed for thin as well as thick YBCO films, and at two very differenttemperatures (76 and 4 K). The reversible effect is dependent on temperature and magnetic field,thus indicating its intrinsic nature. We also report an enhancement of the irreversible strain limitεirr where the reversible strain effect ends and YBCO cracking starts. The value ofεirr increases from about 0.4% to more than 0.5% when YBCO coated conductors arefabricated with an additional Cu protection layer.