Effects of ionic doping on superconducting properties of melt textured YBa₂(Cu_1-xM_x)₃O_7-δ (M ≤ Co, Ni, Zn or Ga) large grains

The work reported in this paper aims at a better understanding of doping effects on high temperature superconducting YBa₂Cu₃O _7-δ (YBCO or M-doped YBCO), in the form of large grains, fabricated by the top seeded melt-growth process. The study focused on the performance of YBCO large grains doped with Co, Ga, Ni and Zn substituting for the Cu site. The rate of T_c suppression with dopant concentration varies significantly among different dopants. Zn doping shows the highest depression rate, followed by Ni, Ga and Co doping. This we attribute to the fact that Zn and Ni substitute at Cu (2) sites on CuO₂ planes in the lattice, whereas Co and Ga occupy Cu (1) sites along CuO chains and they have different magnetic moments. Trapped field, levitation force and J_c are enhanced due to pinning caused by local suppressed superconducting regions, and the enhancement effects are the highest in the case of Zn doping.