High critical current density YBa/sub 2/Cu/sub 3/O/sub 7-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/sub c/ of the YBCO films formed on BaSnO/sub 3//NiO/Ni substrate by pulsed laser deposition reached 0.45 MA/cm/sup 2/ (77 K, 0 T), and J/sub c/ of YBCO/BaZrO/sub 3//NiO/Ni increased up to 0.89 MA/cm/sup 2/ (77 K, 0 T). Development of J/sub 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.