Structure of Fe-doped Y1Ba2Cu3OY and Bi2Ca1Cu2OY

The high-temperature superconductors Y1Ba2(Cu 1-xFex)3Oy and Bi2Sr2 Ca1(Cu1-xFex)2Oy were investigated by x-ray diffraction and Mossbauer experiments, resistivity measurements and thermogravimetrical analysis. The authors report that in the doped 123 compound the preferred substitution of Fe on the Cu (I) site does not affect the superconducting transition Tc at low Fe content much, but leads to an attraction of additional oxygen and to the formation of a microdomain structure. In the Bi-compound the substitution of Fe in the Cu-O2 planes immediately leads to a reduction of Tc and to systematically structural changes. In this structure several different Fe-environments exist as well