The direct evaluation of the internal strain of biaxially textured YBCO film in a coated conductor using synchrotron radiation

The internal strain state of the superconducting film in a coated conductor should be clarified to understand the strain effect on the critical current ( I c ). We have developed an in situ strain measurement technique using synchrotron radiation for YBa 2 Cu 3 O 7−δ (YBCO) coated conductor, and the internal strain of the YBCO film was directly evaluated. YBCO powder obtained from the film in the coated conductor was used as a reference of the zero-strain state. Shifts of the Bragg peaks of the (020) plane of the YBCO film were measured under applied tensile strain, and the internal strain was calculated from the change in the interplanar spacing. The residual strain of the YBCO film in this coated conductor at room temperature (RT) was directly determined to be −0.061%. The fracture strain of the YBCO film was also evaluated from the relationship between the applied strain and the internal strain of YBCO. Surface observation of the coated conductor suggests that fracture initiates in the MgO buffer layer. The irreversible strain (ε irr ) determined by I c –strain characteristics at 77 K was compared with the result from in situ strain measurement. The validity of our technique using synchrotron radiation is discussed.