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

Abstract

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.