title: Tungsten Bronze Barium Neodymium Titanate (Ba(6-3n)Nd(8+2n)Ti(18)O(54)): An Intrinsic Nanostructured Material and Its Defect Distribution.
abstract: We investigated the structure of the tungsten bronze barium neodymium titanates Ba(6-3n)Nd(8+2n)Ti(18)O(54), which are exploited as microwave dielectric ceramics. They form a complex nanostructure, which resembles a nanofilm with stacking layers of ∼12 Å thickness. The synthesized samples of Ba(6-3n)Nd(8+2n)Ti(18)O(54) (n = 0, 0.3, 0.4, 0.5) are characterized by pentagonal and tetragonal columns, where the A cations are distributed in three symmetrically inequivalent sites. Synchrotron X-ray diffraction and electron energy loss spectroscopy allowed for quantitative analysis of the site occupancy, which determines the defect distribution. This is corroborated by density functional theory calculations. Pentagonal columns are dominated by Ba, and tetragonal columns are dominated by Nd, although specific Nd sites exhibit significant concentrations of Ba. The data indicated significant elongation of the Ba columns in the pentagonal positions and of the Nd columns in tetragonal positions involving a zigzag arrangement of atoms along the b lattice direction. We found that the preferred Ba substitution occurs at Nd[3]/[4] followed by Nd[2] and Nd[1]/[5] sites, which is significantly different to that proposed in earlier studies. Our results on the Ba(6-3n)Nd(8+2n)Ti(18)O(54) "perovskite" superstructure and its defect distribution are particularly valuable in those applications where the optimization of material properties of oxides is imperative; these include not only microwave ceramics but also thermoelectric materials, where the nanostructure and the distribution of the dopants will reduce the thermal conductivity.
authors.affiliation: School of Materials, University of Manchester , M13 9PL, U.K.
authors.forename: Feridoon
authors.initials: F
authors.lastname: Azough
authors.affiliation: School of Materials, University of Manchester , M13 9PL, U.K.
authors.forename: Robert Joseph
authors.initials: RJ
authors.lastname: Cernik
authors.affiliation: SuperSTEM, SciTech Daresbury , Keckwick Lane, Warrington WA4 4AD, U.K.|SUPA School of Physics and Astronomy, University of Glasgow , Glasgow G12 8QQ, U.K.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Schaffer
authors.affiliation: School of Materials, University of Manchester , M13 9PL, U.K.|SuperSTEM, SciTech Daresbury , Keckwick Lane, Warrington WA4 4AD, U.K.
authors.forename: Demie
authors.initials: D
authors.lastname: Kepaptsoglou
authors.affiliation: SuperSTEM, SciTech Daresbury , Keckwick Lane, Warrington WA4 4AD, U.K.
authors.forename: Quentin Mathieu
authors.initials: QM
authors.lastname: Ramasse
authors.affiliation: SUPA School of Physics and Astronomy, University of Glasgow , Glasgow G12 8QQ, U.K.
authors.forename: Marco
authors.initials: M
authors.lastname: Bigatti
authors.affiliation: SUPA School of Physics and Astronomy, University of Glasgow , Glasgow G12 8QQ, U.K.
authors.forename: Amir
authors.initials: A
authors.lastname: Ali
authors.affiliation: SUPA School of Physics and Astronomy, University of Glasgow , Glasgow G12 8QQ, U.K.
authors.forename: Ian
authors.initials: I
authors.lastname: MacLaren
authors.affiliation: Central Facility for Electron Microscopy, RWTH Aachen University , Ahornstr. 55, 52064 Aachen, Germany.
authors.forename: Juri
authors.initials: J
authors.lastname: Barthel
authors.affiliation: Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, U.K.
authors.forename: Marco
authors.initials: M
authors.lastname: Molinari
authors.affiliation: Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, U.K.
authors.forename: Jakub Dominik
authors.initials: JD
authors.lastname: Baran
authors.affiliation: Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, U.K.
authors.forename: Stephen Charles
authors.initials: SC
authors.lastname: Parker
authors.affiliation: School of Materials, University of Manchester , M13 9PL, U.K.
authors.forename: Robert
authors.initials: R
authors.lastname: Freer