Influence of iron addition on the oxygen-deficient Sr0.85Bi0.15Co1−xFexO3−δ (0.0⩽x⩽1.0) perovskites

A series of oxygen-deficient Sr0.85Bi0.15Co1−xFexO3−δ (0.0⩽x⩽1.0) perovskite phases were prepared using solid-state reaction. Results of neutron powder diffraction analyses show that the introduction of Fe onto the B-site severely effects the long range coherence of the oxygen vacancy ordered, I4/mmm supercell, observed for the x=0.0 sample. For x=0.1 a smaller, a=b≈ap, c≈2ap, P4/mmm supercell gives the best agreement to the diffraction data, whilst phases in the range 0.2⩽x⩽0.6 adopt disordered cubic perovskite structures. Pseudo-cubic, a=b≈ap, c≈ap, structures are found for x⩾0.8. Evidence of weak superstructures, reflecting local oxygen ordering, is also obtained from electron diffraction. For all oxygen-annealed phases the average structure reverts to cubic Pm3¯m. The as-prepared samples show G-type antiferromagnetic order at room temperature. The oxygen annealed x=0.10, 0.25 and 1.0 samples display low-temperature spin-glass transitions.