title: Crystal Structure, Defects, Magnetic and Dielectric Properties of the Layered Bi3n+1Ti7Fe3n-3O9n+11Perovskite-Anatase Intergrowths.
abstract: The Bi3n+1Ti7Fe3n-3O9n+11materials are built of (001)pplane-parallel perovskite blocks with a thickness of n (Ti,Fe)O6octahedra, separated by periodic translational interfaces. The interfaces are based on anatase-like chains of edge-sharing (Ti,Fe)O6octahedra. Together with the octahedra of the perovskite blocks, they create S-shaped tunnels stabilized by lone pair Bi3+cations. In this work, the structure of the n = 4-6 Bi3n+1Ti7Fe3n-3O9n+11homologues is analyzed in detail using advanced transmission electron microscopy, powder X-ray diffraction, and Mössbauer spectroscopy. The connectivity of the anatase-like chains to the perovskite blocks results in a 3apperiodicity along the interfaces, so that they can be located either on top of each other or with shifts of ±apalong [100]p. The ordered arrangement of the interfaces gives rise to orthorhombic Immm and monoclinic A2/m polymorphs with the unit cell parameters a = 3ap, b = bp, c = 2(n + 1)cpand a = 3ap, b = bp, c = 2(n + 1)cp- ap, respectively. While the n = 3 compound is orthorhombic, the monoclinic modification is more favorable in higher homologues. The Bi3n+1Ti7Fe3n-3O9n+11structures demonstrate intricate patterns of atomic displacements in the perovskite blocks, which are supported by the stereochemical activity of the Bi3+cations. These patterns are coupled to the cationic coordination of the oxygen atoms in the (Ti,Fe)O2layers at the border of the perovskite blocks. The coupling is strong in the n = 3, 4 homologues, but gradually reduces with the increasing thickness of the perovskite blocks, so that, in the n = 6 compound, the dominant mode of atomic displacements is aligned along the interface planes. The displacements in the adjacent perovskite blocks tend to order antiparallel, resulting in an overall antipolar structure. The Bi3n+1Ti7Fe3n-3O9n+11materials demonstrate an unusual diversity of structure defects. The n = 4-6 homologues are robust antiferromagnets below TN= 135, 220, and 295 K, respectively. They show a high dielectric constant that weakly increases with temperature and is relatively insensitive to the Ti/Fe ratio.
authors.affiliation: Electron Microscopy for Material Science (EMAT), University of Antwerp , Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: Dmitry
authors.identifier: http://orcid.org/0000-0002-6384-6690
authors.initials: D
authors.lastname: Batuk
authors.affiliation: Electron Microscopy for Material Science (EMAT), University of Antwerp , Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: Maria
authors.initials: M
authors.lastname: Batuk
authors.affiliation: Chemistry Department, Moscow State University , 119991 Moscow, Russia.
authors.forename: Dmitry S
authors.initials: DS
authors.lastname: Filimonov
authors.affiliation: Physics Department, Moscow State University , 119991 Moscow, Russia.
authors.forename: Konstantin V
authors.initials: KV
authors.lastname: Zakharov
authors.affiliation: Physics Department, Moscow State University , 119991 Moscow, Russia.|Theoretical Physics and Applied Mathematics Department, Ural Federal University , 620002 Ekaterinburg, Russia.|National University of Science and Technology "MISiS″ , 119049 Moscow, Russia.
authors.forename: Olga S
authors.initials: OS
authors.lastname: Volkova
authors.affiliation: Physics Department, Moscow State University , 119991 Moscow, Russia.|Theoretical Physics and Applied Mathematics Department, Ural Federal University , 620002 Ekaterinburg, Russia.|National University of Science and Technology "MISiS″ , 119049 Moscow, Russia.
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Vasiliev
authors.affiliation: Chemistry Department, Moscow State University , 119991 Moscow, Russia.
authors.forename: Oleg A
authors.initials: OA
authors.lastname: Tyablikov
authors.affiliation: Electron Microscopy for Material Science (EMAT), University of Antwerp , Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: Joke
authors.initials: J
authors.lastname: Hadermann
authors.affiliation: Electron Microscopy for Material Science (EMAT), University of Antwerp , Groenenborgerlaan 171, B-2020 Antwerp, Belgium.|Chemistry Department, Moscow State University , 119991 Moscow, Russia.|Skolkovo Institute of Science and Technology , Nobel str. 3, 143026 Moscow, Russia.
authors.forename: Artem M
authors.initials: AM
authors.lastname: Abakumov