Effects of precursor film thickness and heat-treatment temperature on joint rate for a GdBa₂Cu₃O_y superconducting joint

GdBa2Cu3O7-delta (GdBCO) coated conductors (CCs) are promising wire materials because of their high critical temperature and critical current density in magnetic fields. The CCs must contain superconducting joints to create long wires. Previously, we fabricated a GdBCO CC with a superconducting joint by face-to-face crystallization of two CC samples with a GdBCO precursor film. To obtain a high current and low resistance, the crystallinity of GdBCO and a wide joint area are key considerations. This study investigates the effect of the heat-treatment temperature and precursor film thickness on these two factors. GdBCO samples were prepared without or with a precursor film of similar to 50-200 nm thickness via pulsed laser deposition. The samples were set face-to-face and crystallized at 700-820 degrees C under a mechanical pressure of 40 MPa in an electric furnace. X-ray diffraction (XRD) analysis and optical microscopy revealed that both the peak intensity ratio of crystallized GdBCO and the joint rate at 800 degrees C were respectively 1.5 and 1.6 times higher than that at 720 degrees C. As the precursor film thickness increased from 50- 200 nm, the joint rate increased from 15.7- 25.4%, indicating that the heat treatment at similar to 800 degrees C with a thick precursor film, is suitable. The results of this article lead to that the proposed method used in GdBCO CCs to reduce the electrical resistance.