Systematic research on the effect of both positive and negative mismatch dopants in double-doped YBCO superconducting films

We report a novel doping strategy for YBa₂Cu₃O_7-x (YBCO) superconducting films by using a positive mismatch, Ba₂YNbO₆ (BYNO), and a negative mismatch, LaAlO₃ (LAO), simultaneously. Double doping can significantly reduce the c-strain in the YBCO film by canceling the strain between the two dopants. By systematically optimizing the doping amount of both BYNO and LAO, it was found that BYNO and LAO do not act equally. The microstructure and distribution of both BYNO and LAO were investigated with magneto-optic microscopy and scanning electron microscopy. The effect of BYNO and LAO on pinning was confirmed. The results of this study will help select appropriate positive mismatch and negative mismatch dopants, which is fundamental to the design and fabrication of pinning centers to fit different application scenarios.