title: Structural modulation and phase transitions in La2CoO(4.14) investigated by synchrotron X-ray and neutron single-crystal diffraction.
abstract: We report a combined synchrotron X-ray and neutron diffraction study on as-grown La(2)CoO(4.14) single-crystal from 10 to 470 K. Unprecedented structural features in terms of a (3 + 2)D incommensurate modulation have been detected and characterized in the Low Temperature Orthorhombic (LTO) phase already at room temperature despite the complex twinning that was unravelled. A new intermediate phase between the LTO and High Temperature Tetragonal (HTT) phases has been observed for the first time (in the range of 413-433 K). The transformation from LTO to this so-called HTLO (High Temperature Less Orthorhombic) phase is associated to a lowering of orthorhombicity and a loss of one modulation vector, yielding a (3 + 1)D incommensurate modulation. Conversely, above 433 K the HTT phase appears as nonmodulated but exhibits a strong dynamic disorder of CoO(6) octahedra, which has been characterized in detail by reconstruction of nuclear densities via the Maximum Entropy Method (MEM).
authors.affiliation: Institut des Sciences Chimiques de Rennes, Université de Rennes 1, UMR CNRS-UR1 6226, Campus de Beaulieu, Bât 10B, 35042 Rennes Cedex, France.
authors.forename: Loïc
authors.initials: L
authors.lastname: Le Dréau
authors.forename: Carmelo
authors.initials: C
authors.lastname: Prestipino
authors.forename: Olivier
authors.initials: O
authors.lastname: Hernandez
authors.forename: Jürg
authors.initials: J
authors.lastname: Schefer
authors.forename: Gavin
authors.initials: G
authors.lastname: Vaughan
authors.forename: Serge
authors.initials: S
authors.lastname: Paofai
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Perez-Mato
authors.forename: Shoichi
authors.initials: S
authors.lastname: Hosoya
authors.forename: Werner
authors.initials: W
authors.lastname: Paulus