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Title: Metal valences in electron-doped (Sr,La){sub 2}FeTaO{sub 6} double perovskite: A {sup 57}Fe Moessbauer spectroscopy study

Abstract

Substitution of divalent Sr by trivalent La is found to affect the valence states of both of the two B-site cations, Fe and Ta, in the double perovskite oxide (Sr{sub 1-} {sub x} La {sub x} ){sub 2}FeTaO{sub 6}. Moreover, it improves the degree of order of these cations. From {sup 57}Fe Moessbauer spectra the average Fe valence was found to decrease with increasing La substitution level, x. However, the valence of Fe decreased less than expected if the valence of Ta was assumed to remain constant. Hence, we conclude that also the valence of Ta decreases. - Graphical abstract: Both the degree of order and the valence states of Fe and Ta are controlled in the (Sr{sub 1-} {sub x} La {sub x} ){sub 2}FeTaO{sub 6} double perovskite oxide through aliovalent La{sup III}-for-Sr{sup II} substitution.

Authors:
 [1];  [2];  [3];  [1];  [1];  [4]
  1. Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan)
  2. (Finland)
  3. Physics Department, Abo Akademi, FI-20500 Turku (Finland)
  4. (Finland), E-mail: Maarit.Karppinen@tkk.fi
Publication Date:
OSTI Identifier:
21015668
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 2; Other Information: DOI: 10.1016/j.jssc.2006.10.034; PII: S0022-4596(06)00582-2; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CATIONS; DOPED MATERIALS; IRON COMPOUNDS; LANTHANUM COMPOUNDS; MOESSBAUER EFFECT; OXIDES; PEROVSKITE; STRONTIUM COMPOUNDS; TANTALUM COMPOUNDS; VALENCE

Citation Formats

Rautama, E.-L., Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FI-02015 TKK, Linden, J., Yamauchi, H., Karppinen, M., and Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FI-02015 TKK. Metal valences in electron-doped (Sr,La){sub 2}FeTaO{sub 6} double perovskite: A {sup 57}Fe Moessbauer spectroscopy study. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2006.10.034.
Rautama, E.-L., Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FI-02015 TKK, Linden, J., Yamauchi, H., Karppinen, M., & Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FI-02015 TKK. Metal valences in electron-doped (Sr,La){sub 2}FeTaO{sub 6} double perovskite: A {sup 57}Fe Moessbauer spectroscopy study. United States. doi:10.1016/j.jssc.2006.10.034.
Rautama, E.-L., Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FI-02015 TKK, Linden, J., Yamauchi, H., Karppinen, M., and Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FI-02015 TKK. Thu . "Metal valences in electron-doped (Sr,La){sub 2}FeTaO{sub 6} double perovskite: A {sup 57}Fe Moessbauer spectroscopy study". United States. doi:10.1016/j.jssc.2006.10.034.
@article{osti_21015668,
title = {Metal valences in electron-doped (Sr,La){sub 2}FeTaO{sub 6} double perovskite: A {sup 57}Fe Moessbauer spectroscopy study},
author = {Rautama, E.-L. and Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FI-02015 TKK and Linden, J. and Yamauchi, H. and Karppinen, M. and Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, FI-02015 TKK},
abstractNote = {Substitution of divalent Sr by trivalent La is found to affect the valence states of both of the two B-site cations, Fe and Ta, in the double perovskite oxide (Sr{sub 1-} {sub x} La {sub x} ){sub 2}FeTaO{sub 6}. Moreover, it improves the degree of order of these cations. From {sup 57}Fe Moessbauer spectra the average Fe valence was found to decrease with increasing La substitution level, x. However, the valence of Fe decreased less than expected if the valence of Ta was assumed to remain constant. Hence, we conclude that also the valence of Ta decreases. - Graphical abstract: Both the degree of order and the valence states of Fe and Ta are controlled in the (Sr{sub 1-} {sub x} La {sub x} ){sub 2}FeTaO{sub 6} double perovskite oxide through aliovalent La{sup III}-for-Sr{sup II} substitution.},
doi = {10.1016/j.jssc.2006.10.034},
journal = {Journal of Solid State Chemistry},
number = 2,
volume = 180,
place = {United States},
year = {Thu Feb 15 00:00:00 EST 2007},
month = {Thu Feb 15 00:00:00 EST 2007}
}
  • We have employed aliovalent A-site cation substitution, La{sup III}-for-Sr{sup II}, to dope the Sr(Fe{sub 0.5}Ta{sub 0.5})O{sub 3} perovskite oxide with electrons. Essentially single-phase samples of (Sr{sub 1-} {sub x} La {sub x} )(Fe{sub 0.5}Ta{sub 0.5})O{sub 3} were successfully synthesized up to x{approx}0.3 in a vacuum furnace at 1400 deg. C. The samples were found to crystallize (rather than with orthorhombic symmetry) in monoclinic space group P2{sub 1}/n that accounts for the partial ordering of the B-site cations, Fe and Ta. With increasing La-substitution level, x, the degree of Fe/Ta order was found to increase such that the La-richest compositions aremore » best described by the B-site ordered double-perovskite formula (Sr,La){sub 2}FeTaO{sub 6}. From Fe L {sub 3} and Ta L {sub 3} XANES spectra it was revealed that upon electron doping the two B-site cations, Fe{sup III} and Ta{sup V}, are both prone to reduction. Magnetic susceptibility measurements showed spin-glass type behaviour for all the samples with a transition temperature slightly increasing with increasing x. -- Graphical abstract: Valence states of Fe and Ta are controlled in the partially ordered perovskite oxide (Sr,La){sub 2}FeTaO{sub 6}, through aliovalent La{sup III}-for-Sr{sup II} substitu0010ti.« less
  • We describe the preparation and structural characterization by X-ray powder diffraction (XRPD) and Moessbauer spectroscopy of three electron-doped perovskites Sr{sub 3}Fe{sub 2}MoO{sub 9-{delta}} with Fe/Mo = 2 obtained from Sr{sub 3}Fe{sub 2}MoO{sub 9}. The compounds were synthesized by topotactic reduction with H{sub 2}/N{sub 2} (5/95) at 600, 700 and 800 {sup o}C. Above 800 {sup o}C the Fe/Mo ratio changes from Fe/Mo = 2-1 < Fe/Mo < 2. The structural refinements of the XRPD data for the reduced perovskites were carried out by the Rietveld profile analysis method. The crystal structure of these phases is cubic, space group Fm3-bar m,more » with cationic disorder at the two different B sites that can be populated in variable proportions by the Fe atoms. The Moessbauer spectra allowed determining the evolution of the different species formed after the treatments at different temperatures and confirm that Fe ions in the samples reduced at 600, 700 and 800 {sup o}C are only in the high-spin Fe{sup 3+} electronic state.« less
  • The Moessbauer spectra of LaSrYCu{sub 1.97}{sup 57}Fe{sub 0.03}O{sub 6} were measured from room temperature to 5K. Room temperature spectrum is a paramagnetic doublet, and IS and QS values suggest that high spin Fe{sup 3+} are in octahedral site provided by a excess oxygen, similar to La{sub 2}SrCu{sub 2}O{sub 6}. Below 210K, Moessbauer spectra become broad, and consist of paramagnetic doublet and magnetic sextet in the wide temperature range. Temperature variation of H{sub hf} suggest that the Neel temperature lies above 200 K. The irreversibility and field dependence of susceptibility are observed at low temperatures. By combining the results of themore » Moessbauer spectra and magnetic measurements, these behaviors are explained as superparamagnetism of the antiferro spin clusters, and at low temperatures, clusters freeze to the cluster glass like state.« less
  • The structure, thermal, and electrical properties of double perovskite material Sr{sub 2}(Fe,Ti)O{sub 6} at high temperature have been studied. This material was synthesized by a solid state reaction method. X-ray diffraction characterization at room temperature for all samples shows a single phase and having a structure of cubic double perovskite with Pm3m space group. The variation of Fe and Ti atoms are seen in an increasing of lattice parameter and grain size which is found between 30 nm and 80 nm. The electrical properties as a function of temperature and frequency are characterized by using RLC-meter with impedance spectroscopy method. The impedancemore » data are presented in Nyquist and Bode plot resulting in the equivalent circuit and its parameters. The equivalent circuit shows the effect of grain and grain boundary in the electrical properties of materials. DC conductivity of Sr{sub 2}(Fe,Ti)O{sub 6} as a function of temperature was explained by using Arrhenius equation. The value of the activation energy which is evaluated from dc conductivity as a function of temperature shows the effect of grain and grain boundary. The activation energy exhibits of oxygen vacancy in Sr{sub 2}(Fe,Ti)O{sub 6} which is also supported by morphology of Sr{sub 2}(Fe,Ti)O{sub 6} is characterized by field emission scanning electron microscopy (FESEM).« less