Site occupancy and Tc degradation in iron substituted YBa2(Cu1−xFex)4O8+δ

Mössbauer study of the (Ru1-xFex)Sr2GdCu2O8-δ system and two of its possible impurities: SrRuO3 and Gd2CuO4

“…These facts and previous results and calculations [29] for different oxygen environments of Fe atoms in the Y123 and Y124 structures allow the following proposal for the Fe site assignment in the Ru1212 structure: Doublet A, that has a similar ΔQ (≈ 0.9 mm/s) to the ΔQ value of the doublet associated with Fe 3+ with five-fold pyramidal coordination in the Cu(1) sites of the Y123 or Y124 structures, can be reasonably associated with the Iron concentration x corresponding Ru site of the Ru1212 structure, considering that the O-Ru bond-lengths of the later do not significantly differ from either of the former. On the other hand, the only surroundings compatible with the high ΔQ (≈ 1.70 mm/s) value of doublet C would turn out to be Fe 3+ in four-fold (planar) coordination in the Ru sites.…”

“…Sufficient arguments have been put forward to sustain that the ΔQ≈0.6 mm/s doublet (doublet B in our case) must be associated with Fe in the Cu(2) sites of the structure, in five-fold pyramidal coordination [29] and, although the small value of its IS suggests that the charge state of iron in this site should be +2, the joint values of the IS and ΔQ do not allow a conclusive assignment of the charge-state of Fe.…”

Effect of Mn doping on the specific heat of the highTCsuperconductor REBa2Cu3Oy(RE = Y,Gd)

“…Several investigators have carried out substitution experiments in high T C superconductors, which has helped further understanding of the mechanism of superconductivity as well as improving the magnetic properties, like flux pinning etc, in order to enhance the applicability of these materials. In particular, substituting transition metal elements, for example Zn, Fe, Ni and Co, for Cu dramatically affects the superconducting and normal state properties [1][2][3][4][5][6][7][8]. Different impurities have preferential occupancies due to the presence of two copper sites in these high T C superconductors, a plane and a chain.…”

“…Different impurities have preferential occupancies due to the presence of two copper sites in these high T C superconductors, a plane and a chain. Dopants like Fe and Co occupy plane sites with an accompanying orthorhombic to tetragonal structural transformation [1][2][3]. However no such transformation is observed for Zn and Ni that occupy chain sites [4][5][6][7][8].…”

Suppression of Tc in the (Y0.9Ca0.1)Ba2Cu4$minus$xFexO8 system

“…2. In this inset, the T c variation with x for this system compared with the YBa2Cu4 -x Fe x O 8 (Y124Fe) [7] and YBa 2 Cu 3-x Fe x O y (Y123Fe) [8,9] systems. We observed that the T c values in YCa124Fe system are larger than those reported in the reference [7].…”