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

Abstract

The brownmillerite phase LaSrCoFeO₅ has been prepared by partially reducing the parent perovskite material LaSrCoFeO₆ in 10% H₂/N₂. 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 LaSrCoFeO_5.58 are synthesized by fluorination and room temperature air oxidation of LaSrCoFeO₅, respectively. LaSrCoFeO_5.56 could be prepared by quenching the sample from 1300 °C into liquid nitrogen. Neutron powder diffraction data, Mössbauer 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.