Abstract
The effects of Fe substitution for Cu in Bi1.6Pb0.4Sr1.6Ca2Cu3O10−y were investigated. The superconducting transition, phase assemblage, and lattice parameters were studied for samples with up to ~1/4 of the Cu replaced by Fe. With increasing levels of Fe, the superconducting transition gradually degenerated to that of semiconducting behaviour, the phase assemblage underwent the reaction series 2223→2221→2201, and the c-axis of the 2212 phase decreased monotonically when the doped samples were heat treated in air. These results can be explained in terms of structural changes rather than magnetic effects, where the higher valence and smaller size of Fe3+ compared Cu2+ alter the nature of the oxygen co-ordination and bonding. When the Fe-doped samples were treated in nitrogen, the effect of destabilisation of the superconducting phase was minimised. In contrast to the effect of Fe on the structure, the depression in Tc is attributed mainly to the magnetic effects of Fe doping. The critical concentration of the Fe dopant at which superconductivity was completely destroyed, is at ~13% Cu replacement.
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