Greatly enhanced flux pinning properties of fluorine-free metal–organic decomposition YBCO films by co-addition of halogens (Cl, Br) and metals (Zr, Sn, Hf)

Additive-free YBCO films, as well as those with halogen (X) added, metal (M) added and (X, M) co-added, have been prepared by the fluorine-free metal–organic decomposition method on SrTiO₃(100) single crystalline substrates, where X = Cl, Br and M = Zr, Sn, Hf. It was revealed that the addition of both Cl and Br to the starting solution resulted in the generation of oxyhalide, Ba₂Cu₃O₄ X ₂, in the YBCO films, and that the oxyhalide was found to promote the bi-axial orientation of the YBCO crystals. By adding a decent amount of Cl or Br, highly textured YBCO films with high J _c were reproducibly obtained, even when an impurity metal, M, was co-added, while the addition of M without X did not greatly improve J _c owing to the poor bi-axial orientation of the YBCO crystals. Our results suggest that the addition of Br more effectively enhances J _c than the addition of Cl. The pinning force density at 40 K in 4.8 T reached ∼55 GN m⁻³ with the co-addition of (Br, M). This value is much larger than that of the pure YBCO film, reaching ∼17 GN m⁻³. (paper)