Mössbauer spectroscopy of Hg-1223 superconductors

Doping of (Hg0.3Pb0.4)(Sr0.8Ba0.2)2Ca2Cu3Oy superconductors with the Mössbauer nuclei 57Fe and 119Sn was investigated. EDX analysis showed that 57Fe entered the superconducting phase. The introduction of Fe into the superconductor led to a decrease in the Tc(0)-values from 112 K for the undoped to 105 K for the Fe-doped phase. Low concentrations of Fe were also present in the Ca-Sr-Cu-O phase. Sn formed a separate secondary phase, predominately barium stannate with some Sr, Ca, Pb, Cu and low amounts of Fe. Small amounts of Sn were also present in the Sr-Ca-Cu-O secondary phase. The 57Fe Mössbauer spectra were interpreted under the assumption that Fe occupies the square pyramidal five-fold oxygen coordinated Cu sites and the square planar four-fold oxygen coordinated Cu sites in the superconducting phases. The 119Sn Mössbauer spectra mainly reflected the Sn environment in the Sn-rich secondary phase.