LaSrCoFeO5, LaSrCoFeO5F and LaSrCoFeO5.5: new La-Sr-Co-Fe perovskites

The brownmillerite phase LaSrCoFeO5 has been prepared by partially reducing the parent perovskite material LaSrCoFeO6 in 10% H-2/N-2. The material crystallizes in the Icmm space group with the transition metal ions randomly distributed over the octahedral and tetrahedral sites of the structure. The material shows G-type antiferromagnetic order at room temperature which is consistent with the presence of high spin Co2+ and Fe3+. The perovskite phases LaSrCoFeO5F and LaSrCoFeO5.58 are synthesized by fluorination and room temperature air oxidation of LaSrCoFeO5, respectively. LaSrCoFeO5.56 could be prepared by quenching the sample from 1300 degrees C into liquid nitrogen. Neutron powder diffraction data, Mossbauer spectroscopy and magnetic susceptibility measurements suggest a G-type antiferromagnetism in these materials at room temperature due to the presence of Co3+ in the high spin state, which is not common in this type of materials.