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
₃
O
_7-δ
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 aaxis of REBCO aligns along the longitudinal direction of REBCO-CC, f
_A
, up to ≅ 90%when a compressive bending strain of ≅ -1.35%is applied along the longitudinal direction. We found that f
_A
evaluated by repeated X-ray diffraction measurements decreases over time if the domain-controlled REBCO-CCs with a high f
_A
value is kept flat, whereas f
_A
remains high if the sample remains bent. In addition, we also observed that f
_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
_A
probably leads to changes in the superconducting properties, and may become important for the design of REBCO pancake coils.