Abstract
57Fe Mossbauer spectroscopy was used to study the effects of heavy ion irradiation on (Bi0.93Pb0.17)Sr1.9Ca2.05(Cu1.02Fe0.01)3Oy superconductors. The Mossbauer spectra of the irradiated superconductor showed significant changes in the subspectra belonging to different Cu microenvironments into which Fe ions were substituted. The relative occurrence of Fe occupying the square pyramidal fivefold oxygen coordinated Cu sites decreased while Fe3+ substituting the square planar fourfold oxygen coordinated Cu sites increased upon bombardment by 246 MeV 86Kr8+ ions. This observation was interpreted on the basis of partial replacement of the apical oxygen atoms in the square pyramids surrounding one of the Cu sites. Such oxygen vacancies create additional square planar coordination sites for Cu. These results also support the covalent character of Cu-O bonds in the superconducting layer as well as the ionic character of bond of apical oxygen to Cu.
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