title: Characterization of Ordering in A-Site Deficient Perovskite Ca1-xLa2x/3TiO3Using STEM/EELS.
abstract: The vacancy ordering behavior of an A-site deficient perovskite system, Ca1-xLa2x/3TiO3, was studied using atomic resolution scanning transmission electron microscopy (STEM) in conjunction with electron energy-loss spectroscopy (EELS), with the aim of determining the role of A-site composition changes. At low La content (x = 0.2), adopting Pbnm symmetry, there was no indication of long-range ordering. Domains, with clear boundaries, were observed in bright-field (BF) imaging, but were not immediately visible in the corresponding high-angle annular dark-field (HAADF) image. These boundaries, with the aid of displacement maps from A-site cations in the HAADF signal, are shown to be tilt boundaries. At the La-rich end of the composition (x = 0.9), adopting Cmmm symmetry, long-range ordering of vacancies and La3+ions was observed, with alternating La-rich and La-poor layers on (001)pplanes, creating a double perovskite lattice along the c axis. These highly ordered domains can be found isolated within a random distribution of vacancies/La3+, or within a large population, encompassing a large volume. In regions with a high number density of double perovskite domains, these highly ordered domains were separated by twin boundaries, with 90° or 180° lattice rotations across boundaries. The occurrence and characteristics of these ordered structures are discussed and compared with similar perovskite systems.
authors.affiliation: University of Oxford , Department of Materials, Parks Road, Oxford OX1 3PH, U.K.
authors.forename: Mohsen
authors.initials: M
authors.lastname: Danaie
authors.affiliation: SuperSTEM Laboratory, SciTech Daresbury Campus , Keckwick Ln, Warrington WA4 4AD, U.K.
authors.forename: Demie
authors.initials: D
authors.lastname: Kepaptsoglou
authors.affiliation: SuperSTEM Laboratory, SciTech Daresbury Campus , Keckwick Ln, Warrington WA4 4AD, U.K.
authors.forename: Quentin M
authors.initials: QM
authors.lastname: Ramasse
authors.affiliation: National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory , 67 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Colin
authors.initials: C
authors.lastname: Ophus
authors.affiliation: University of Sheffield , Department of Materials Science & Engineering, Immobilisation Science Laboratory, Mappin Street, Sheffield S1 3JD, U.K.|School of Engineering, University of Liverpool , Brownlow Hill, Liverpool L69 3GH, U.K.
authors.forename: Karl R
authors.initials: KR
authors.lastname: Whittle
authors.affiliation: University of Sheffield , Department of Materials Science & Engineering, Immobilisation Science Laboratory, Mappin Street, Sheffield S1 3JD, U.K.
authors.forename: Sebastian M
authors.initials: SM
authors.lastname: Lawson
authors.affiliation: University of Oxford , Department of Materials, Parks Road, Oxford OX1 3PH, U.K.
authors.forename: Stella
authors.initials: S
authors.lastname: Pedrazzini
authors.affiliation: University of Oxford , Department of Materials, Parks Road, Oxford OX1 3PH, U.K.
authors.forename: Neil P
authors.initials: NP
authors.lastname: Young
authors.affiliation: University of Oxford , Department of Materials, Parks Road, Oxford OX1 3PH, U.K.
authors.forename: Paul A J
authors.initials: PA
authors.lastname: Bagot
authors.affiliation: Materials Science & Technology Division, Oak Ridge National Laboratory , 1 Bethel Valley Road, Oak Ridge, Tennessee 37831, United States.
authors.forename: Philip D
authors.initials: PD
authors.lastname: Edmondson