ABSTRACTMössbauer effect and neutron diffraction measurements have been made as a function of composition for YBa2(Cu1−xFex)3O7+δ. A chemically driven disordering of the sublattices is observed with increasing Fe concentration which results in a transition from the orthorhombic to a tetragonal phase. However, as the occupancy of the oxygen site 0(1) in the chain is depleted and the site of the ordered vacancy 0(5) between the chains becomes occupied, the total oxygen content is not reduced but remains near seven in contrast to behavior observed in the quenched tetragonal phases. Mössbauer spectra for x =0.05 at temperatures below 15K show magnetic hyperfine splitting which is characteristic of a spin glass; i.e., a distribution of magnetic fields. It is inferred from Mössbauer results that Fe preferentially occupies the Cu(1) site.
