title: Direct space structure solution from precession electron diffraction data: Resolving heavy and light scatterers in Pb(13)Mn(9)O(25).
abstract: The crystal structure of a novel compound Pb(13)Mn(9)O(25) has been determined through a direct space structure solution with a Monte-Carlo-based global optimization using precession electron diffraction data (a=14.177(3)A, c=3.9320(7)A, SG P4/m, R(F)=0.239) and compositional information obtained from energy dispersive X-ray analysis and electron energy loss spectroscopy. This allowed to obtain a reliable structural model even despite the simultaneous presence of both heavy (Pb) and light (O) scattering elements and to validate the accuracy of the electron diffraction-based structure refinement. This provides an important benchmark for further studies of complex structural problems with electron diffraction techniques. Pb(13)Mn(9)O(25) has an anion- and cation-deficient perovskite-based structure with the A-positions filled by the Pb atoms and 9/13 of the B positions filled by the Mn atoms in an ordered manner. MnO(6) octahedra and MnO(5) tetragonal pyramids form a network by sharing common corners. Tunnels are formed in the network due to an ordered arrangement of vacancies at the B-sublattice. These tunnels provide sufficient space for localization of the lone 6s(2) electron pairs of the Pb(2+) cations, suggested as the driving force for the structural difference between Pb(13)Mn(9)O(25) and the manganites of alkali-earth elements with similar compositions.
authors.affiliation: EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium. joke.hadermann@ua.ac.be
authors.forename: Joke
authors.initials: J
authors.lastname: Hadermann
authors.forename: Artem M
authors.initials: AM
authors.lastname: Abakumov
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Tsirlin
authors.forename: Vladimir P
authors.initials: VP
authors.lastname: Filonenko
authors.forename: Julie
authors.initials: J
authors.lastname: Gonnissen
authors.forename: Haiyan
authors.initials: H
authors.lastname: Tan
authors.forename: Johan
authors.initials: J
authors.lastname: Verbeeck
authors.forename: Mauro
authors.initials: M
authors.lastname: Gemmi
authors.forename: Evgeny V
authors.initials: EV
authors.lastname: Antipov
authors.forename: Helge
authors.initials: H
authors.lastname: Rosner