Moessbauer study of high-Tc superconductor Bi2Sr2Ca1-xYx(Cu1-y57Fey)2O8+z

Fe57 Moessbauer effects are measured at room temperature for the samples of high-Tc superconductor Bi2Sr2Ca1-xYx(Cu0.97Fe0.0357)2O8+z. The observed spectra can be divided into three doublet spectra, D1, D2 and D3; D1 and D2 come from the Fe57 probe surrounded by 5 oxygens like pyramidal and by 6-oxygen octahedron, respectively, and D3 comes from impurity phase. We have found that with hole reduction, the isomer shifts (IS) increase while their quadruple splitting (Eq) decrease almost linearly. Each of IS and Eq is analyzed by the increase of shield effect for nuclear charge and decrease of electric field gradient at nucleus due to the increase of Fe-3d electrons, respectively. This analysis reveals that the electrons in Fe-3d orbital increase by Δn = 0.08 with increase of x = 0 to 1. (orig.)