The synthesis, structures and properties of doped Y-Ba-Cu-M-O and Bi-Sr-Ca-Cu-O high Tc phases

Homogeneous YBa2Cu3-xMxO7-y (M = Fe,Co,Al,Ni and Zn) and Bi2Sr2Can-1CunOy (n = 1,2 and 3) phases have been synthesized and characterized with respect to their structural, magnetic, and superconducting properties. The authors find that the oxygen content in the doped Y-based materials is dependent upon the nature and amount of doping, and reaches values greater than 7 for the Co and Fe-doped samples. Both the Fe and Co-doped systems undergo an orthorhombic-tetragonal structural transition with increased doping (x). Evidence for the site at which the metal substitution takes place is obtained by means of thermogravimetric analysis and neutron diffraction measurements. Independent of the dopant (M), Tc decreases with increasing x and a correlation between the changes in Tc and bond lengths is shown. The structure and properties of the superconducting bismuth phases with n = 1,2 and 3 are described, and compared to those of the Y-based materials