Force free strain exerted on a YBCO layer at 77 K in surround Cu stabilized YBCO coated conductors

The stress/strain behavior of the surround Cu stabilized YBCO coated conductors and its influence on critical current were precisely investigated. The internal strain exerted on the superconducting YBCO layer was determined at 77 K by using a neutron diffraction technique at JAEA. The initial compressive strain decreased during tensile loading and changed to a tensile component at the force free strain (Aff), where the internal uniaxial stress becomes zero in the YBCO layer. The Aff was evaluated to be 0.19–0.21% at 77 K. The critical current measurements were carried out under a uniaxial tensile load at 77 K. The strain dependence revealed a characteristic behavior, where a maximum was observed at 0.035%. Thus it was made clear that the strain at the critical current maximum does not correlate with Aff for YBCO coated conductors.