The effect of oxygen stoichiometry on phase relations and structure in the system La[sub 1[minus]x]Sr[sub x]FeO[sub 3[minus][sigma]] (0 [le] x [le] 1, 0 [le] [sigma] [le] 0. 5)

Journal Article · Tue Mar 01 04:00:00 EST 1994 · Journal of Solid State Chemistry; (United States)

DOI:https://doi.org/10.1006/jssc.1994.1083· OSTI ID:6622469

Dann, S E; Currie, D B; Weller, M T ^[1]; Thomas, M F; Al-Rawwas, A D ^[2]

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1. Univ. of Southampton (United Kingdom)
2. Univ. of Liverpool (United Kingdom)

An extensive range of compounds in the La[sub 1[minus]x]Sr[sub x]FeO[sub 3[minus][sigma]] (0 [le] x [le] 1, 0 [le] [sigma] [le] 0.5) system have been synthesized. When [sigma] [approximately] 0 the system is composed of three crystallographically different regions: Orthorhombic for 0 [le] x [le] 0.2, rhombohedral for 0.4 [le] x [le] 0.7, and cubic for 0.8 [le] x [le] 1.0. Products were characterized by thermogravimetric analysis and Moessbauer spectroscopy yielding information on oxygen stoichiometry and iron oxidation state. At 4.2 K, Moessbauer spectra are composed of magnetic sextet components arising from different charge states of iron; in the orthorhombic and rhombohedral phases the charge states Fe[sup 3+] and Fe[sup 5+] coexist, and Fe[sup 4+] and Fe[sup 3+] are present in the cubic region. Room temperature Moessbauer spectra show that samples in the orthorhombic region are still magnetically ordered and the coexistence of Fe[sup 3+] and Fe[sup 5+] remains, while between x = 0.4 and x = 1.0 the samples are paramagnetic; in the rhombohedral region the spectra show the presence of Fe[sup 4+] and Fe[sup 3+], and in the cubic region both Fe[sup 4+] and an intermediate valence state are assigned. High-resolution powder neutron diffraction data were collected on samples annealed under high-pressure oxygen, and full structure refinements were carried out using the Rietveld method. Accurate bond length data obtained for all phases show that the iron coordination geometry becomes more regular with increasing Sr, and hence Fe[sup 4+], content. A phase diagram for the full range of lanthanum/strontium and oxygen stoichiometry is proposed.

• OSTI ID: 6622469
• Journal Information: Journal of Solid State Chemistry; (United States), Journal Name: Journal of Solid State Chemistry; (United States) Vol. 109:1; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
ALKALINE EARTH METAL COMPOUNDS
BOND LENGTHS
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMICAL PREPARATION
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CUBIC LATTICES
DIAGRAMS
DIMENSIONS
GRAVIMETRIC ANALYSIS
IRON COMPOUNDS
IRON OXIDES
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
LENGTH
MOESSBAUER EFFECT
ORTHORHOMBIC LATTICES
OXIDES
OXYGEN COMPOUNDS
PHASE DIAGRAMS
PHASE STUDIES
QUANTITATIVE CHEMICAL ANALYSIS
RARE EARTH COMPOUNDS
STOICHIOMETRY
STRONTIUM COMPOUNDS
STRONTIUM OXIDES
SYNTHESIS
THERMAL ANALYSIS
THERMAL GRAVIMETRIC ANALYSIS
TRANSITION ELEMENT COMPOUNDS
TRIGONAL LATTICES
VALENCE