title: A vacancy-disordered, oxygen-deficient perovskite with long-range magnetic ordering: local and average structures and magnetic properties of Sr2Fe1.5Cr0.5O5.
abstract: The local and average crystal structures and magnetic properties of the oxygen-deficient perovskite Sr(2)Fe(1.5)Cr(0.5)O(5+y) were studied using powder X-ray and neutron diffraction, neutron-pair distribution function analysis, and electron energy-loss spectroscopy. This material crystallizes in the cubic Pm3m space group, with a = 3.94491(14) Å. The oxygen vacancies are distributed randomly throughout the perovskite-type structure, and the average coordination number of the Fe(Cr) sites is 5. Refinement of the neutron diffraction data indicates y ∼ 0.05. This is in discordance with an earlier report on a material with the same nominal composition and cell constant. Electron energy-loss Cr L(2,3)-edge spectroscopy shows that Cr(3+) is present, which is also contrary to previous speculation. Neutron-pair distribution function studies show that a brownmillerite-like model involving ordered vacancies and alternating octahedral and tetrahedral coordination at the metal sites, gives a better description of the local structure out to ∼5 Å. A remarkable phenomenon determined by neutron diffraction in Sr(2)Fe(1.5)Cr(0.5)O(5) is the occurrence of a long-range G-type antiferromagnetic ordering with T(c) ≈ 565 K because cubic oxygen-deficient perovskites with B-site disorder usually do not undergo transitions to magnetically ordered states. The observation of long-range antiferromagnetic order and the T(c) value are in accordance with previous Mössbauer spectroscopic studies.
authors.affiliation: Department of Chemistry, McMaster University, Hamilton, Canada L8S 4M.
authors.forename: Farshid
authors.initials: F
authors.lastname: Ramezanipour
authors.forename: John E
authors.initials: JE
authors.lastname: Greedan
authors.forename: Joan
authors.initials: J
authors.lastname: Siewenie
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Donaberger
authors.forename: Stuart
authors.initials: S
authors.lastname: Turner
authors.forename: Gianluigi A
authors.initials: GA
authors.lastname: Botton