Chlorine doped Y123 thin films have been successfully prepared by the fluorine-free metal organic decomposition (FF-MOD) method on SrTiO 3 (100) single crystal substrates. The rectangular Ba 2 Cu 3 O 4 Cl 2 (Ba2342) columns were epitaxially grown in the film without degrading crystallinity and transition temperature (T c ) of Y123. Cl-doped Y123 films maintained high T c of 90.5-91.5 K and they showed higher critical current density (J c ) than the Cl-free films particularly in magnetic fields. The high J c feature was observed in thick films up to ∼0.93 μm in thickness. In addition, Cl and Hf co-doped Y123 films maintained high crystallinity and showed further improved J c of 1.1 MA cm −2 at 40 K under 5 T. These suggested that Ba2342 precipitates have two effects on FF-MOD processed Y123 films. One is an increase in pinning force and the other is improvement of crystallinity of Y123 because of the good lattice matching between Y123 and Ba2342.

Undoped, Cl-doped, (Cl, Hf) co-doped and (Cl, Sn) co-doped YBa2Cu3Oy (YBCO) thin films have been prepared by the fluorine-free metal–organic decomposition (FF-MOD) method on SrTiO3(100) single-crystalline substrates. Cross-sectional microstructures of these films were investigated in detail using scanning transmission electron microscopy (STEM). Rectangular-shaped oxychloride precipitates (Ba2Cu3O4Cl2) and fine particles (BaSnO3) were clearly observed in the (Cl, Sn) co-doped films. The magnetic angular dependence of the critical current density (Jc–H–θ) of these films was evaluated. The existence of c-axis-correlated type pinning centers was suggested in Cl-containing YBCO films, whereas this type of pinning is not common in MOD-processed films. Jc values were enhanced by Cl doping and further by (Cl, Sn) co-doping in all magnetic field directions at 77 K. This improved Jc–H–θ property with c-axis-correlated pinning sites is the first report in FF-MOD-processed YBCO films.

The synthesis conditions of fluorine-free metal–organic decomposition (FF-MOD)-processed YBa2Cu3O y (YBCO) films on buffered metallic substrates have been systematically investigated. Chlorine addition to the starting solution was found to be quite effective for expanding the synthesis conditions of highly c-axis-oriented YBCO films. YBCO films showing a high critical current, ∼100 A/cm (77 K, ∼0 T), were successfully obtained by sintering at 740 °C, which is ∼50 °C lower than the typical sintering temperature for FF-MOD-processed YBCO films. This strongly indicated that chlorine addition is promising for the development of long and homogeneous YBCO tapes even by sintering at a low temperature of ∼740 °C.

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We improved the critical current properties of fluorine-free metal organic decomposition processed YBCO thin films prepared on buffered metallic substrates by increasing the thickness of the films. YBCO films prepared using a conventional one-time growth exhibit a maximum Ic (77 K, ∼0 T) value of ∼100 A per 1 cm width for a film with a thickness of 0.8 μm, and Ic decreases with further increases in the film thickness due to the generation of impurity particles and micro-cracks. In this study, a multiple growth process was adopted for the preparation of thick films to avoid these problems. The Ic of films prepared using this method monotonically increased with the film thickness. YBCO films with a thickness of ∼3.0 μm recorded a quite high Ic (77 K, ∼0 T) value for ∼210 A cm−1 width. Additionally, the in-field Jcs at 20 K and 40 K were found to increase almost proportionally to the film thickness.