Studies on Non-Stoichiometric Strontium Ferrate, SrFeO3-X
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).
KeywordsOxygen Vacancy Acta Cryst Tetragonal Distortion Tetragonal Unit Cell Stoichiometric Material
Unable to display preview. Download preview PDF.
- 6.J. M. Hutchison and A. J. Jacobson, to be publishedGoogle Scholar
- 10.M. Zanne and C. Gleitzer, Bull Soc. Chim. France, p1567 (1971)Google Scholar
- 13.A. J. Jacobson, Acta Cryst B32, 1087 (1976).Google Scholar
- 14.J. B. Goodenough and J. M. Longo, in “Landolt-Google Scholar
- Bornstein, Numerical Data and Functional Data in Science and Technology“. New Series (K. H. Hellwege, Ed.), Group III, Vol. 4a, p. 131. Springer-Verlag, New York (1970).Google Scholar
- 15.M. Zanne and C. Gleitzer, J. Solid State Chem., 6, 163 (1973) 16 M. Zanne, C. Gleitzer and J. Aubry, J. Solid State Chem., 14, 160 1 1975 )Google Scholar
- 19.C. Greaves, D. Phil Thesis, University of Oxford (1973)Google Scholar
- 21.B. W. Dale and B. C. Tofield, unpublishedGoogle Scholar