Mossbauer study of the oxygen order and superconductivity in Y₁₋ₓ Prₓ Ba₂ (Cu₀.₉₉Fe₀.₀₁)₃ O[sub y]
Mossbauer effect measurements at ⁵⁷Fe nuclei have been made at room temperature on Y₁₋ₓ Prₓ Ba₂ (Cu₀.₉₉Fe₀.₀₁)₃ O[sub y] with x = 0, 0.1, 0.2, 0.4, 0.5, 0.6, and 0.7. Neutron diffraction experiments show that iron atoms substitute into the Cul sites in the orthorhombic phase, and into interstitial places on the Cul planes in the tetragonal phase. There were no significant changes in the Mossbauer parameters, isomer shifts, areas, or electric quadrupole splittings except △EQ1 and △EQ3 as the Pr concentration was increased. △EQ1 showed inconsistent change. △EQ3 had a minimum value at X=0.4 where the superconducting-to-superconducting transition occurred. This minimum for the △EQ3 pattern was similar to the case of the Sr doping in the Ba site in the YBaCuO compounds. Rapid depression of Tc when increasing the Pr concentration was observed. From these results, it is suggested that the Cu2-0 planes play the major role in determining the high Tc in the YBaCuO compounds , rather than the Cul-0 chains. These Mossbauer results also demonstrate that the Y sites are well isolated from the Cul-0 chains in the YBaCuO compounds.