High critical current density YBa2Cu3O7-x films grown on mechanically polished surface-oxidized NiO/Ni substrates

A NiO surface produced by surface-oxidation epitaxy (SOE) method was flattened by a mechanical polishing technique. The surface roughness of NiO was reduced in this manner to about 5 nm. In addition, thin perovskite films were deposited on the polished NiO as a new cap layer. Consequently, J_c of the YBCO films formed on BaSnO₃/NiO/Ni substrate by pulsed laser deposition reached 0.45 MA/cm² (77 K, 0 T), and J_c of YBCO/BaZrO₃/NiO/Ni increased up to 0.89 MA/cm² (77 K, 0 T). Development of J_c is due to the reduction of superconducting weak coupling by flattening of NiO surfaces and the improvement of crystal orientation of YBCO films by the use of perovskite cap layers.