Bismuth cuprate high-Tc superconductors using cationic substitution

Effect of Er/Y addition on the growth and superconductivity of Bi2212 films

In order to increase the critical current density of Bi2212 superconducting films to broaden their application areas. A series of Bi₂Sr₂CaCu₂O_8+δ-xRE₂O₃ (RE = Er/Y) (x = 0, 0.04, 0.08, 0.12, 0.16, 0.20) thin films were prepared by the sol-gel method. The structure, morphology and superconductivity of the RE₂O₃ doping films were characterized in detail. The effect of RE₂O₃ on the superconductivity of Bi2212 superconducting films was investigated. It was shown that the Bi2212 films were (00l) epitaxially grown. The in-plane orientation relationship between the Bi2212-xRE₂O₃ and the SrTiO₃ was Bi2212[100](001)//SrTiO₃[011](100). The grain size in the out-of-plane direction of Bi2212 tends to increase with the amount of RE₂O₃ doping. Doping with RE₂O₃ had no significant effect on the anisotropy of Bi2212 crystal growth, but inhibited the agglomerative growth of the precipitated phase on the surface to a certain extent. Furthermore, the conclusion was that the superconducting transition temperature (T_c,onset) was almost unaffected, while the zero resistance transition temperature (T_c,zero) continued to decrease with increasing doping level. The thin film samples Er2 (x = 0.04) and Y3 (x = 0.08) exhibited the best current-carrying capacity in magnetic fields.

On the Origin of the Structural Modulation in the Bi Cuprates As Derived from 3d-Metal Substituted Phases

A substitution for Cu by a 3d-metal (Fe, Co, Mn) in the superconducting Bi phases (Bi2Sr2Can−1CunOy; n = 1,2 and 3) has led to the discovery of new phases. These 3d-metal substituted phases are non-superconducting and, in contrast to the Cu-based phases, they exhibit a structural modulation that is commensurate. Single crystal x-ray studies were performed on the Bi2Sr3Fe2Oy, Bi2Sr2CoOy and Bi2Sr2MnOy compounds. A result, in common, is that the modulation is caused by the periodic insertion of a row of oxygen atoms in the Bi layers and this results in a corrugated-like slab structure. The Bi-O layers can be described as composed of alternating rocksalt-type and oxygen deficient perovskite-type blocks. For the Fe (n=2) phase the Bi atoms form ribbons (chains) in the ab plane. This is in contrast to the n=1 Co or Mn phases for which a disorder at the oxygen position is observed. Although the extra oxygen in the Bi-O layer could account for the doping mechanism in the high Tc Bi-phases, cation non-stoichiometry may also beimportant.