Promotion of Epitaxial Growth and Enhanced Jc by Coaddition of Br and Metals (Zr, Sn, Hf) to the Fluorine-Free MOD Processed YBCO Films

Coaddition of Br and metals (M), where M = Zr, Sn, Hf, was attempted for YBCO films prepared by the fluorine-free metal-organic decomposition method. It was revealed that Br-addition, which subsequently forms textured Ba
₂
Cu
₃
O
₄
Br
₂
oxybromides in the film, promotes the biaxial alignment of the YBCO crystals. Although M-addition did not improve Jc owing to the serious degradation of crystallinity, (Br, M)-coaddition was found to largely enhance flux pinning properties by the suppression of the random crystal growth. The pinning force density at 40 K in 4.8 T reached ~62 GN/m
³
for (Br, M)-coadded YBCO films. This value is more than three times large compared to that of additive-free YBCO films.