In-Plane Domain Control of REBCO Coated Conductors by Annealing under Bending Strain

We attempted to control the volume fraction of the in-plane domains of REBa$_{2}$Cu$_{\bf 3}$O$_{\bf 7-\delta }$coated conductors (REBCO-CCs) by annealing under a bending strain applied at high temperature. We succeeded in changing the volume fraction of the region where the $a$axis of REBCO aligns along the longitudinal direction of REBCO-CC, $f_{\rm A}$, up to $\simeq\! 90\%$when a compressive bending strain of $\simeq\! -1.35\%$is applied along the longitudinal direction. We found that $f_{\rm A}$evaluated by repeated X-ray diffraction measurements decreases over time if the domain-controlled REBCO-CCs with a high $f_{\rm A}$value is kept flat, whereas $f_{\rm A}$remains high if the sample remains bent. In addition, we also observed that $f_{\rm A}$in the as-received sample increases over time if the sample is exposed to a compressive bending strain at room temperature. These results suggest that oxygen atoms can migrate in REBCO even at room temperature when a uniaxial strain is applied to the REBCO-CC. Such a temporal variation of $f_{\rm A}$probably leads to changes in the superconducting properties, and may become important for the design of REBCO pancake coils.