title: Complex cation order in anion-deficient Ba(n)YFe(n-1)O(2.5n) perovskite phases.
abstract: The synthesis and structural characterization of BanYFen-1O2.5n (n = 2, 3, 4) anion-deficient perovskite phases is reported. The n = 2 and n = 3 members of the series, Ba2YFeO5 and Ba3YFe2O7.5, adopt structures which consist of ordered arrays of corner-linked YO6 octahedra and FeO4 tetrahedra on the perovskite B-sites and are described in unit cells related to a simple cubic perovskite cell by respective 2√2 × √2 × 2 and 3√2 × √2 × 2 geometric expansions. The complex cation ordering schemes observed in the two phases can be described on the basis of Y2Fe2O10□2 secondary building units. A rationalization for the observed structures is presented on the basis of the need to minimize lattice strain while maintaining the integrity of the local YO6 and FeO4 coordination polyhedra. The n = 4 member of the series, Ba4YFe3O10, adopts a cation and anion-vacancy disordered structure, which is attributed to dilution of the structure directing effects at extreme Y:Fe stoichiometric ratios. Magnetization data indicate Ba2YFeO5 and Ba3YFe2O7.5 exhibit paramagnetic behavior, consistent with the lack of a long-range Fe-O-Fe network. Ba4YFe3O10 adopts an antiferromagnetic state below 50 K.
authors.affiliation: Department of Chemistry, University of Oxford , Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, United Kingdom.
authors.forename: Kun
authors.initials: K
authors.lastname: Luo
authors.forename: Michael A
authors.initials: MA
authors.lastname: Hayward