Mössbauer spectroscopy of Hg-1223 superconductors

Abstract

Doping of (Hg 0.3Pb 0.4)(Sr 0.8Ba 0.2) 2Ca 2Cu 3O y superconductors with the Mössbauer nuclei 57 Fe and 119 Sn was investigated. Energy dispersive X-ray (EDX) analysis showed that 57 Fe entered the superconducting phase. The introduction of Fe into the superconductor led to a decrease in the T c(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 57 Fe Mössbauer spectra were interpreted under the assumption that Fe occupies the square pyramidal fivefold oxygen-coordinated Cu sites and the square planar fourfold oxygen-coordinated Cu sites in the superconducting phases. The 119 Sn Mössbauer spectra mainly reflected the Sn environment in the Sn-rich secondary phase.