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Studies on Non-Stoichiometric Strontium Ferrate, SrFeO3-X

  • Bruce C. Tofield

Abstract

The oxide perovskites SrMO3,where M is a first-row transition metal,are interesting in that a number of the end members have,unusually,an undistorted simple cubic perovskite structure at room temperature, and also because wide ranges of oxygen non-stoichiometry have been reported for several systems. The most detailed study of the SrFeO3-x system (0 ≤ x ≤ 0.5) reported previously was by MacChesney et al who were the first to prepare the stoichiometric material using high pressures of oxygen, (1). SrFeO3.00 was obtained after equilibration at 550 C and 5,000 psi for one week, or at 335°C and 13,000 psi for 16 hours. Samples containing more than 30% Fe3+ (SrFeO2.84 to SrFeO2.72) were reported to have a simple tetragonal distortion of the cubic unit cell, but no superlattice formation was observed. Below SrFeO 2.72, a two-phase mixture of a perovskite-like phase and a bown-millerite-like phase (SrFeO2.50) was found. Gallagher et al assumed from X-ray powder data that SrFeO2.50 (and BaFeO2.50) were isostructural with CaFeO2.50 (space group Pcmn) (2, 3, 4). MacChesney et al also studied the BaFeO3-x system (5), which is complicated by the presence of mixed hexagonal and cubic stacking of octahedra, although, unlike the oxygen vacancy ordering in SrFeO2.75 such behaviour is readily revealed by X-ray powder diffraction and has been directly imaged in the electron microscope (6). Several different phases in the BaFeO2.5-3.0 region have been observed (7–12) but the only solved structure is the 6H form (cch stacking as in hexagonal barium titanate), determined neutron diffraction (13).

Keywords

Oxygen Vacancy Acta Cryst Tetragonal Distortion Tetragonal Unit Cell Stoichiometric Material 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer Science+Business Media New York 1977

Authors and Affiliations

  • Bruce C. Tofield
    • 1
  1. 1.Materials Physics DivisionA.E.R.E.Harwell OxfordshireEngland

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