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New Twists on the Perovskite Theme: Crystal Structures of the Elusive Phases R and S of NaNbO3

DOI: 10.1021/ic3006585 DOI Help

Authors: Martin D. Peel (School of Chemistry and EaStCHEM, University of St. Andrews) , Stephen P. Thompson (Diamond Light Source) , Aziz Daoud-aladine (ISIS Facility, Rutherford Appleton Laboratory) , Sharon E. Ashbrook (School of Chemistry and EaStCHEM, University of St. Andrews) , Philip Lightfoot (School of Chemistry and EaStCHEM, University of St. Andrews)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Inorganic Chemistry , VOL 51 (12) , PAGES 6876-6889

State: Published (Approved)
Published: June 2012
Diamond Proposal Number(s): 6108

Abstract: The crystal structure of NaNbO3 has been studied in detail in the temperature regime 360 < T < 520 °C using a combination of high-resolution neutron and synchrotron X-ray powder diffraction, supported by first-principles calculations. A systematic symmetry-mode analysis is used to determine the presence of the key active distortion modes that, in turn, provides a small and an unambiguous set of trial structural models. A unique model for Phase S (480 < T < 510 °C) is elucidated, having a 2 × 2 × 4 superlattice of the aristotype perovskite structure, space group Pmmn. This unusual and unique structure features a novel example of a compound octahedral tilt system in a perovskite. Two possible structural models for Phase R (370 < T < 470 °C) are determined, each having a 2 × 2 × 6 superlattice and differing only in the nature of the complex tilt system along the ‘long’ axis. It is impossible to identify a definitive model from the present study, although reasons for preferring one over the other are discussed. Some of the possible pitfalls in determining such complex, pseudosymmetric crystal structures from powder diffraction data are also highlighted.

Subject Areas: Chemistry


Instruments: I11-High Resolution Powder Diffraction

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