TY - JOUR

T1 - Spin-state transition of iron in (Ba0.5 Sr0.5) (Fe0.8 Zn0.2) O3 - δ perovskite

AU - Feldhoff, Armin

AU - Martynczuk, Julia

AU - Arnold, Mirko

AU - Myndyk, Maxym

AU - Bergmann, Ingo

AU - Šepelák, Vladimir

AU - Gruner, Wolfgang

AU - Vogt, Ulrich

AU - Hähnel, Angelika

AU - Woltersdorf, Jörg

N1 - Funding Information: We would like to thank Prof. Harald Behrens for putting his high-pressure apparatus at our disposal and Dr. Falk Heinroth for assistance in TGA measurements. Our discussions with Profs. Jürgen Caro and Haihui Wang were fruitful and are appreciated. This work was financially supported by the Deutsche Forschungsgemeinschaft (DFG) under Grant FE 928/1-2. V.Ŝ. thanks the DFG for supporting his work in the framework of the Priority Program “Crystalline Nonequilibrium Phases” (SPP 1415). Partial support by the Alexander von Humboldt Foundation, the APVV (0728-07), and the VEGA (2/0065/08) is gratefully acknowledged.

PY - 2009/11

Y1 - 2009/11

N2 - 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 Mössbauer spectroscopical in situ methods. At room temperature, the iron in (Ba0.5 Sr0.5) (Fe0.8 Zn0.2) O3 - δ (BSFZ) is in a mixed valence state of 75% Fe4 + in the high-spin state and 25% Fe3 + predominantly in the low-spin state. When heated to 900 {ring operator} C, a slight reduction of iron is observed that increases the quantity of Fe3 + 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 {ring operator} C making this ceramic highly attractive for intermediate temperature applications (500 - 800 {ring operator} C).

AB - 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 Mössbauer spectroscopical in situ methods. At room temperature, the iron in (Ba0.5 Sr0.5) (Fe0.8 Zn0.2) O3 - δ (BSFZ) is in a mixed valence state of 75% Fe4 + in the high-spin state and 25% Fe3 + predominantly in the low-spin state. When heated to 900 {ring operator} C, a slight reduction of iron is observed that increases the quantity of Fe3 + 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 {ring operator} C making this ceramic highly attractive for intermediate temperature applications (500 - 800 {ring operator} C).

KW - EELS

KW - Mössbauer spectroscopy

KW - Perovskite

KW - Spin-state

KW - Valence

UR - http://www.scopus.com/inward/record.url?scp=70350571375&partnerID=8YFLogxK

U2 - 10.1016/j.jssc.2009.07.058

DO - 10.1016/j.jssc.2009.07.058

M3 - Article

AN - SCOPUS:70350571375

VL - 182

SP - 2961

EP - 2971

JO - Journal of solid state chemistry

JF - Journal of solid state chemistry

SN - 0022-4596

IS - 11

ER -