Fe-site occupancy and superconductivity in Y1−zCazBa2(Cu1−xFex)3O6+y

Abstract

X-ray diffraction and 57Fe Mössbauer spectroscopy studies show that partial substitution of Ca for Y in Y1−zCazBa2(Cu1−xFex)3O6+y (0.05≤z≤0.15, 0.003≤x≤0.20) result in increased Fe solubility and a larger percentage of Fe occupancy of the Cu(2) plane site (prepared conventionally). Materials with z≳0.00 have a slightly depressed superconducting transition onset temperature Tc relative to the z=0.00 compounds. It is also shown that Fe occupancy of the Cu(2) site in Y1−zCazBa2(Cu1−xFex)3O6+y can be substantially increased when these materials are treated at high temperatures in inert atmospheres followed by oxygenation at low temperatures. Tc decreases more rapidly in these latter materials compared to the conventionally prepared ones. Implications concerning ordered Fe-cluster formation and superconducting pair breaking in the Cu(2) site are drawn.