Mossbauer study of the oxygen order and superconductivity in Y(Ba₁-ₓSrₓ)₂(Cu₀.₉₉Fe₀.₀₁)₃Oy
⁵⁷Fe Mossbauer effect measurements have been performed at room temperature on Y(Ba₁-ₓSrₓ)₂(Cu₀.₉₉Fe₀.₀₁)₃O[sub y] with x from 0 to 1. In all samples, four quadrupole splittings, corresponding to iron atoms in different local sites, are observed. The Mossbauer spectra for low Sr concentrations resemble those for 1% Fe doping in the high temperature orthorhombic oxide, YBa₂(Cu₀.₉₉Feo.01₀.₀₁)₃O₇ The experimental neutron diffraction results show that iron atoms substitute principally into the Cul site or an interstitial site near Cul in YBa₂ (Cu₁-ₓFeₓ)₃O₇. The strontium ion is smaller than the barium ion so that a lattice distortion, or defects, may occur and additional oxygen vacancies may be introduced. This would lead to the depression of T[sub c] in the Y(Ba₁-ₓSrₓ)₂(Cu₀.₉₉Fe₀.₀₁)₃O[sub y] series.