Preparation of double-layer REBa2Cu3O7−δ tapes for enhancing engineering current density by Ag-diffusion bonding

Second-generation high-temperature superconducting (2G-HTS) tapes with high engineering critical current densities (J_e) are widely used in engineering and technology applications. This study introduced a twisting device that successfully layered two REBa₂Cu₃O_7−δ films onto a single substrate. Heating the twisting device to above 600 °C induced Ag-diffusion bonding at the interface between the two tapes. A thin film pressure sensor detected a silver layer pressure of about 6.5 MPa. After the oxygen annealing treatment, a current increase of 81.7 A was observed using the four-probe method, which was a 1.5-fold enhancement over the original tape current, and the J_e was increased from 560 A/mm² to 790 A/mm² at 77 K. The use of reverse bending annealing effectively improved the flexibility of the DHOS conductors. Through microanalysis, it was observed that the bonding between MgO and Y₂O₃ in the buffer layer was weak, resulting in the detachment of LaMnO₃ and MgO together with the superconducting layer. The exfoliated buffer layer prevented oxygen penetration, adversely affecting the performance of the double HTS layers on one substrate (DHOS). Moreover, the coverage of the buffer layer increases with the number of layers complicating the complete peeling of the superconducting layer. Further detailed studies point out the direction of improvement for future work in preparing multilayer conductors.