Study of Columnar Defect Formation in MOD YBCO Film Using Chemical Doping

This paper describes a promising route to introduce columnar defects into YBCO films by chemical doping process. A series of Y₂O₃ and BaZrO₃ doped YBCO films were fabricated by a TFA_MOD process. The J_c of Y₂O₃ doped YBCO film was found to be larger than that of pure YBCO film at all fields though no columnar defects were observed. On the other hand, high density nanoscale Zr enriched columnar defects were successfully achieved in Zr-doped YBCO. The size of these defects was as small as 10 nm. Effects of heat treatment temperatures (760^degC ~ 820^degC), dwell times (0.5 h ~ 3 h) and partial pressures of oxygen (0 ~ 1%) on defects formation in BaZrO₃ doped YBCO were investigated. It was found that the formation of columnar defects depends on process conditions. Films with such nanoscale columnar defects exhibited a significant enhancement of J_c at all fields. Maximum pinning force density exceeding 8 GN m^-3 was obtained in 5% BZO-doped YBCO films.