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Title: Crystal structures, charge and oxygen-vacancy ordering in oxygen deficient perovskites SrMnO{sub x} (x < 2.7).

Abstract

Bulk SrMnOx samples with oxygen contents 2.5x<2.7 have been studied using a combination of neutron time-of-flight and high-energy high-resolution synchrotron X-ray diffraction measurements along with thermogravimetric analysis. We report the identification and characterization of two new oxygen-vacancy ordered phases, Sr5Mn5O13 (SrMnO2.6-tetragonal P4/m a=8.6127(3) Angstroms, c=3.8102(2)Angstroms) and Sr7Mn7O19 (SrMnO2.714-monoclinic P2/m a=8.6076(4)Angstroms, b=12.1284(4)Angstroms, c=3.8076(2)Angstroms, {gamma}=98.203(2) degrees). The nuclear and magnetic structures of Sr2Mn2O5 are also reported (SrMnO2.5 nuclear: orthorhombic Pbam, magnetic: Orthorhombic Ay type Pcbam with cM=2c). In the three phases, oxygen-vacancies are ordered in lines running along one of the (100) directions of the parent cubic perovskite system. Oxygen-vacancy ordering allows the charge and orbital ordering of the Mn3+ and Mn4+ cations in the new phases.

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC); National Science Foundation (NSF)
OSTI Identifier:
914915
Report Number(s):
ANL/MSD/JA-58358
Journal ID: ISSN 0022-4596; JSSCBI; TRN: US0804844
DOE Contract Number:
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Solid State Chem.; Journal Volume: 180; Journal Issue: 5 ; May 2007
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE; 43 PARTICLE ACCELERATORS; CATIONS; CRYSTAL STRUCTURE; NEUTRONS; OXYGEN; PEROVSKITE; PEROVSKITES; SYNCHROTRONS; THERMAL GRAVIMETRIC ANALYSIS; X-RAY DIFFRACTION

Citation Formats

Suescun, L., Chmaissem, O., Mais, J., Dabrowski, B., Jorgensen, J. D., Materials Science Division, and Northern Illinois Univ.. Crystal structures, charge and oxygen-vacancy ordering in oxygen deficient perovskites SrMnO{sub x} (x < 2.7).. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2007.03.020.
Suescun, L., Chmaissem, O., Mais, J., Dabrowski, B., Jorgensen, J. D., Materials Science Division, & Northern Illinois Univ.. Crystal structures, charge and oxygen-vacancy ordering in oxygen deficient perovskites SrMnO{sub x} (x < 2.7).. United States. doi:10.1016/j.jssc.2007.03.020.
Suescun, L., Chmaissem, O., Mais, J., Dabrowski, B., Jorgensen, J. D., Materials Science Division, and Northern Illinois Univ.. Tue . "Crystal structures, charge and oxygen-vacancy ordering in oxygen deficient perovskites SrMnO{sub x} (x < 2.7).". United States. doi:10.1016/j.jssc.2007.03.020.
@article{osti_914915,
title = {Crystal structures, charge and oxygen-vacancy ordering in oxygen deficient perovskites SrMnO{sub x} (x < 2.7).},
author = {Suescun, L. and Chmaissem, O. and Mais, J. and Dabrowski, B. and Jorgensen, J. D. and Materials Science Division and Northern Illinois Univ.},
abstractNote = {Bulk SrMnOx samples with oxygen contents 2.5x<2.7 have been studied using a combination of neutron time-of-flight and high-energy high-resolution synchrotron X-ray diffraction measurements along with thermogravimetric analysis. We report the identification and characterization of two new oxygen-vacancy ordered phases, Sr5Mn5O13 (SrMnO2.6-tetragonal P4/m a=8.6127(3) Angstroms, c=3.8102(2)Angstroms) and Sr7Mn7O19 (SrMnO2.714-monoclinic P2/m a=8.6076(4)Angstroms, b=12.1284(4)Angstroms, c=3.8076(2)Angstroms, {gamma}=98.203(2) degrees). The nuclear and magnetic structures of Sr2Mn2O5 are also reported (SrMnO2.5 nuclear: orthorhombic Pbam, magnetic: Orthorhombic Ay type Pcbam with cM=2c). In the three phases, oxygen-vacancies are ordered in lines running along one of the (100) directions of the parent cubic perovskite system. Oxygen-vacancy ordering allows the charge and orbital ordering of the Mn3+ and Mn4+ cations in the new phases.},
doi = {10.1016/j.jssc.2007.03.020},
journal = {J. Solid State Chem.},
number = 5 ; May 2007,
volume = 180,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}
  • Bulk SrMnO {sub x} samples with oxygen contents 2.5{<=}x<2.7 have been studied using a combination of neutron time-of-flight and high-energy high-resolution synchrotron X-ray diffraction measurements along with thermogravimetric analysis. We report the identification and characterization of two new oxygen-vacancy ordered phases, Sr{sub 5}Mn{sub 5}O{sub 13} (SrMnO{sub 2.6}-tetragonal P4/m a=8.6127(3) A, c=3.8102(2) A) and Sr{sub 7}Mn{sub 7}O{sub 19} (SrMnO{sub 2.714}-monoclinic P2/m a=8.6076(4) A, b=12.1284(4) A, c=3.8076(2) A, {gamma}=98.203(2){sup o}). The nuclear and magnetic structures of Sr{sub 2}Mn{sub 2}O{sub 5} are also reported (SrMnO{sub 2.5} nuclear: orthorhombic Pbam, magnetic: Orthorhombic Ay type P{sub c}bam with c {sub M}=2c). In the three phases,more » oxygen-vacancies are ordered in lines running along one of the (100) directions of the parent cubic perovskite system. Oxygen-vacancy ordering allows the charge and orbital ordering of the Mn{sup 3+} and Mn{sup 4+} cations in the new phases. - Graphical abstract: The structures of Sr{sub 5}Mn{sub 5}O{sub 13} and Sr{sub 7}Mn{sub 7}O{sub 19} (shown) were determined using synchrotron X-rays and neutron time-of-flight powder diffraction and the Rietveld method on multiphase bulk samples. Charge, orbital and oxygen vacancy-ordering has been observed in the novel compounds where Mn{sup 4+} octahedra and Mn{sup 3+} pyramids are linked through the corners leaving lines of vacant oxygen sites lying along the c-axis.« less
  • Ten compounds belonging to the series of oxygen-deficient perovskite oxides Ca2Fe2 xMnxO5 and CaSrFe2 xMnxO5+y, where x = 1/2, 2/3, and 1 and y 0 0.5, were synthesized and investigated with respect to the ordering of oxygen vacancies on both local and long-range length scales and the effect on crystal structure and magnetic properties. For the set with y 0 the oxygen vacancies always order in the long-range sense to form the brownmillerite structure containing alternating layers of octahedrally and tetrahedrally coordinated cations. However, there is a change in symmetry from Pnma to Icmm upon substitution of Sr for onemore » Ca for all x, indicating local Td chain (vacancy) disorder. In the special case of CaSrFeMnO5 the neutron diffraction peaks broaden, indicating only short-range structural order on a length scale of 160 . This reveals a systematic progression from Ca2FeMnO5 (Pnma, well-ordered tetrahedral chains) to CaSrFeMnO5 (Icmm, disordered tetrahedral chains, overall short-range order) to Sr2FeMnO5 (Pm3m, destruction of tetrahedral chains in a long-range sense). Systematic changes occur in the magnetic properties as well. While long-range antiferromagnetic order is preserved, the magnetic transition temperature, Tc, decreases for the same x when Sr substitutes for one Ca. A review of the changes in Tc for the series Ca2Fe2 xMxO5, taking into account the tetrahedral/octahedral site preferences for the various M3+ ions, leads to a partial understanding of the origin of magnetic order in these materials in terms of a layered antiferromagnetic model. While in all cases the preferred magnetic moment direction is (010) at low temperatures, there is a cross over for x = 0.5 to (100) with increasing temperature for both the Ca2Fe2 xMnxO5 and the CaSrFe2 xMnxO5 series. For the y > 0 phases, while a brownmillerite ordering of oxygen vacancies is preserved for the Ca2 phases, a disordered Pm3m cubic perovskite structure is always found when Sr is substituted for one Ca. Long-range magnetic order is also lost, giving way to spin glass or cluster-glass-like behavior below 50 K. For the x = 0.5 phase, neutron pair distribution function (NPDF) studies show a local structure related to brownmillerite ordering of oxygen vacancies. Neutron diffraction data at 3.8 K show a broad magnetic feature, incommensurate with any multiple of the chemical lattice, and with a correlation length (magnetic domain) of 6.7(4) .« less
  • A family of Sr-doped perovskite compounds Ln{sub 1-x}Sr {sub x}CoO{sub 3-{delta}} (Ln = La{sup 3+}, Pr{sup 3+} and Nd{sup 3+}; x > 0.60), were prepared by sol-gel chemistry and reaction at 1100 deg. C under 1 atm of oxygen. This structural family has been shown to be present only for rare earth ions larger than Sm{sup 3+} and an upper limit of Sr{sup 2+} solubility in these phases was found to exist between x = 0.90 and 0.95. X-ray diffraction shows oxygen-deficient, simple cubic (Pm-3m) perovskite crystal structures. The combination of electron and powder neutron diffraction reveals that oxygen vacancymore » ordering occurs, leading to a tetragonal (P4/mmm) superstructure and a doubling of the basic perovskite unit along the crystallographic c-axis. No additional Ln{sup 3+}/Sr{sup 2+} cation ordering was observed.« less
  • Neutron diffractions studies reveal the presence of oxygen disorder in the oxygen deficient perovskites Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba). Synchrotron X-ray studies demonstrate that these oxides have a double perovskite-type structure with the cell size increasing as the size of the B cation increases from 8.2114(2) A for B=Ca to 8.4408(1) A for B=Ba. It is postulated that a combination of local clustering of the anions and vacancies together with water-water and water-host hydrogen bonds plays a role in defining the volume of the encapsulated water clusters and that changes in the local structure upon heating result in anomalousmore » thermal expansion observed in variable temperature diffraction measurements. - Graphical abstract: The oxides Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba) have unusual anion disorder. There is a lag in the contraction in the cell size of Sr{sub 2}CaSbO{sub 5.5}nH{sub 2}O established from X-ray diffraction measurements following the loss of water suggesting changes on the local structure are important. Highlights: > The average structures of the defect perovskites Sr{sub 2}MSbO{sub 5.5} established. > Anion and cation disorder quantified by neutron and synchrotron X-ray diffraction. > Anomalous thermal expansion due to local clustering of anions and vacancies observed.« less
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