Spin-state transition of iron in (Ba{sub 0.5}Sr{sub 0.5})(Fe{sub 0.8}Zn{sub 0.2})O{sub 3-{delta}} perovskite

Journal Article · Sun Nov 15 00:00:00 EST 2009 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.07.058· OSTI ID:21372373

Feldhoff, Armin ^[1]; Martynczuk, Julia; Arnold, Mirko ^[1]; Myndyk, Maxym; Bergmann, Ingo; Sepelak, Vladimir ^[2]; Gruner, Wolfgang ^[3]; Vogt, Ulrich ^[4]; Haehnel, Angelika; Woltersdorf, Joerg ^[5]

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1. Institut fuer Physikalische Chemie und Elektrochemie, Leibniz Universitaet Hannover, D-30167 Hannover (Germany)
2. Institut fuer Physikalische und Theoretische Chemie, Technische Universitaet Braunschweig, D-38104 Braunschweig (Germany)
3. Leibniz-Institut fuer Festkoerper- und Werkstoffforschung Dresden, D-01069 Dresden (Germany)
4. EMPA, Materials Science and Technology, CH-8600 Duebendorf (Switzerland)
5. Max-Planck-Institut fuer Mikrostrukturphysik, D-06120 Halle (Germany)

The redox behavior of iron during heating of a high-performance perovskite for ceramic oxygen separation membranes was studied by combined electron energy-loss (EELS, esp. ELNES) and Moessbauer spectroscopical in situ methods. At room temperature, the iron in (Ba{sub 0.5}Sr{sub 0.5})(Fe{sub 0.8}Zn{sub 0.2})O{sub 3-{delta}} (BSFZ) is in a mixed valence state of 75% Fe{sup 4+} in the high-spin state and 25% Fe{sup 3+} predominantly in the low-spin state. When heated to 900 deg. C, a slight reduction of iron is observed that increases the quantity of Fe{sup 3+} species. However, the dominant occurrence is a gradual transition in the spin-state of trivalent iron from a mixed low-spin/high-spin to a pure high-spin configuration. In addition, a remarkable amount of hybridization is found in the Fe-O bonds that are highly polar rather than purely ionic. The coupled valence/spin-state transition correlates with anomalies in thermogravimetry and thermal expansion behavior observed by X-ray diffraction and dilatometry, respectively. Since the effective cationic radii depend not only on the valence but also on the spin-state, both have to be considered when estimating under which conditions a cubic perovskite will tolerate specific cations. It is concluded that an excellent phase stability of perovskite-based membrane materials demands a tailoring, which enables pure high-spin states under operational conditions, even if mixed valence states are present. The low spin-state transition temperature of BSFZ provides that all iron species are in a pure high-spin configuration already above ca. 500 deg. C making this ceramic highly attractive for intermediate temperature applications (500-800 deg. C). - At room temperature, the iron in a high-performance perovskite for ceramic oxygen separation membranes is in a mixed valence state of 75% Fe{sup 4+} in the high-spin state and 25% Fe{sup 3+} predominantly in the low-spin state. When heated to 900 deg. C, a slight reduction of iron is observed that increases the quantity of Fe{sup 3+} species. However, the dominant occurrence is a gradual transition in the spin-state of trivalent iron from a mixed low-spin/high-spin to a pure high-spin configuration.

• OSTI ID: 21372373
• Journal Information: Journal of Solid State Chemistry, Vol. 182, Issue 11; Other Information: DOI: 10.1016/j.jssc.2009.07.058; PII: S0022-4596(09)00345-4; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BARIUM COMPOUNDS
CERAMICS
ENERGY-LOSS SPECTROSCOPY
HIGH SPIN STATES
IRON COMPOUNDS
IRON IONS
MOESSBAUER EFFECT
OXIDES
PEROVSKITE
PHASE STABILITY
SPIN
STRONTIUM COMPOUNDS
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
THERMAL GRAVIMETRIC ANALYSIS
TRANSITION TEMPERATURE
X-RAY DIFFRACTION
ZINC COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
ANGULAR MOMENTUM
CHALCOGENIDES
CHARGED PARTICLES
CHEMICAL ANALYSIS
COHERENT SCATTERING
DIFFRACTION
ELECTRON SPECTROSCOPY
ENERGY LEVELS
GRAVIMETRIC ANALYSIS
IONS
MINERALS
OXIDE MINERALS
OXYGEN COMPOUNDS
PARTICLE PROPERTIES
PEROVSKITES
PHYSICAL PROPERTIES
QUANTITATIVE CHEMICAL ANALYSIS
SCATTERING
SPECTROSCOPY
STABILITY
TEMPERATURE RANGE
THERMAL ANALYSIS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS