The local structure and composition of Ba4Nb2O 9-based oxycarbonates

Jana Bezjak, Artem M. Abakumov, Aleksander Renik, Marjeta Maek Krmanc, Botjan Janar, Danilo Suvorov

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14 Citations (Scopus)

Abstract

X-ray powder-diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), infrared spectroscopy (IR), thermogravimetry (TG) and mass spectroscopy (MS) were performed to investigate the composition and the crystal structure of tetra-barium di-niobate (V) Ba 4Nb2O9. The TG, MS and IR studies revealed that the compound is a hydrated oxycarbonate. Assuming that the carbonate stoichiometrically replaces oxygen, the composition of the low-temperature α-modification, obtained by slow cooling from 1100 °C, corresponds to Ba4Nb2O8.8(CO3) 0.2·0.1H2O, while the quenched high-temperature γ-modification has the Ba4Nb2O 8.42(CO3)0.58·0.38H2O composition. The α-phase has a composite incommensurately modulated structure consisting of two mutually interacting [Ba] and the [(Nb,□)O3] subsystems. The composite modulated crystal structure of the α-phase can be described with the lattice parameters a=10.2688(1) , c=2.82426(8) , q=0.66774(2)c (*) and a superspace group R3̄m(00γ)0s. The HRTEM analysis demonstrates the nanoscale twinning of the trigonal domains parallel to the {1 0 0} crystallographic planes. The twinning introduces a one-dimensional disorder into the [(Nb,□)O3] subsystem, which results in an average P6̄2c crystal structure of the α-phase. Possible places for the carbonate group in the structure are discussed using a comparison with other hexagonal perovskite-based oxycarbonates.

Original languageEnglish
Pages (from-to)1823-1828
Number of pages6
JournalJournal of Solid State Chemistry
Volume183
Issue number8
DOIs
Publication statusPublished - Aug 2010
Externally publishedYes

Keywords

  • 2H-hexagonal perovskite derivatives
  • Incommensurately modulated composite structure
  • Nanoscale twinning
  • One-dimensional disorder
  • Oxycarbonate

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