Takanori Motoki

Dramatic effects of chlorine doping on Jc and microstructure of fluorine-free MOD Y123 thin films

Chlorine doped Y123 thin films have been successfully prepared by the fluorine-free metal organic decomposition (FF-MOD) method on SrTiO3(100) single crystal substrates. The rectangular Ba2Cu3O4Cl2 (Ba2342) columns were epitaxially grown in the film without degrading crystallinity and transition temperature (Tc) of Y123. Cl-doped Y123 films maintained high Tc of 90.5–91.5 K and they showed higher critical current density (Jc) than the Cl-free films particularly in magnetic fields. The high Jc 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 Jc 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.

Microstructures and improved J c–H characteristics of Cl-containing YBCO thin films prepared by the fluorine-free MOD method

Undoped, Cl-doped, (Cl, Hf) co-doped and (Cl, Sn) co-doped YBa2Cu3O y (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 (J c–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. J c values were enhanced by Cl doping and further by (Cl, Sn) co-doping in all magnetic field directions at 77 K. This improved J c–H–θ property with c-axis-correlated pinning sites is the first report in FF-MOD-processed YBCO films.

Critical Current Properties of FF-MOD RE123 Thin Films Sintered for Short Time

Optimizations of sintering conditions, such as PO2 , temperature and time, and the introduction of effective pinning centers were systematically studied to improve the critical current properties of RE123 thin films prepared by fluorine-free (FF) metal organic decomposition (MOD) method. We found that epitaxial growth of Y123 in FF-MOD is extremely fast. Effects of dilute Ga doping, RE mixing, and introduction of BaHfO3 fine particles on flux pinning properties were examined. Dilute Ga doping enhanced Jc at low temperature in high magnetic field regardless of sintering conditions, while BaHfO3 precipitates improved Jc at 77 K. In addition, introduction of undoped Y123 seed layer was found to dramatically improve crystallinity of doped or RE-mixed films. Moreover, high epitaxial growth rate of RE123 was maintained for these films.