Improvement of $J_{\rm c}$ for GdBCO Coated Conductors by Annealing Under Strain

$\hbox{GdBa}_{2}\hbox{Cu}_{3}\hbox{O}_{y}$
coated conductors were annealed under external strain (strain-annealing). The residual strain after annealing was evaluated using synchrotron radiation. We found that the residual strain is changed by the strain-annealing. The volume fraction of the
$a$
-axis domains along the longitudinal direction is increased by compression-annealing and decreased by tension-annealing. In addition, the
$J_{\rm c}$
value of the tension-annealed sample increases drastically below 70 K, although the
$J_{\rm c}$
value is smaller than that of the as-received sample at 77.3 K for
$B//c$
. The peak of the angular dependent
$J_{\rm c}$
at
$\theta = 0^{\circ}$
, which originates from the
$c$
-axis correlated pinning, for the strain-annealed sample is much smaller than that of the as-received sample. It is considered that the shrinking of the
$c$
-axis correlated pinning because of the reduction of the twin structure and the increase of carrier doping may be related to the change in
$J_{ \rm c}$
properties.