Mössbauer study of quadrupole interaction at the different Cu sites in the Bi-system superconductor

Abstract

57Fe Mössbauer measurements have been performed on Fe-doped samples of Bi 1.6Pb 0.4Sr 2Ca 3Cu 4- x Fe x O y ( x=0.06 and 0.08) at room temperature. The Mössbauer spectra show three quadrupole doublets that can be related to different Cu sites. Two doublets (B and C) with larger quadrupole splitting (QS) are assigned with a 57Fe probe atom on the Cu-O square planar sites of the compound with different local charge environments. Another doublet A with smallest quadrupole splitting is associated with a Fe atom in a planar pyramid site. the doublet with smallest QS possesses relatively the smaller area indicating that the Fe atom preferentially occupies a square planar site rather than a pyramid site. To assure our assignment, we calculated the EFG (electric field gradient) on different Cu sites with the use of the point charge model and of the calculation of an effective ions valence.