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Title: Structure and magnetism of 4H-BaMnO{sub 3-x} (0=<x=<0.35) and 4H-Ba{sub 0.5}Sr{sub 0.5}MnO{sub 3-x} (0=<x=<0.21)

Abstract

The synthesis and structure determination of 4H-BaMnO{sub 3-x} (0=<x=<0.35) and 4H-Ba{sub 0.5}Sr{sub 0.5}MnO{sub 3-x} (0=<x=<0.21) is described. Neutron powder diffraction data unambiguously show the anion vacancies in the oxygen-deficient phases lie in the hexagonal BaO{sub 3-x} layers, rather than the cubic layers predicted by previous structural models. The localization of anion vacancies in the hexagonal layers is discussed on the basis of the local co-ordination polyhedra of the metal cations. Low-temperature neutron diffraction data show the oxidized materials adopt antiferromagnetic ordered structures (Ba{sub 0.5}Sr{sub 0.5}MnO{sub 2.99}: T{sub N}=265K). Anion-deficient phases do not achieve magnetic order suggesting the Mn(III/IV) charge disorder suppresses long-range magnetic order.

Authors:
 [1];  [2]
  1. Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QR (United Kingdom)
  2. Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QR (United Kingdom). E-mail: michael.hayward@chem.ox.ac.uk
Publication Date:
OSTI Identifier:
20784832
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 179; Journal Issue: 1; Other Information: DOI: 10.1016/j.jssc.2005.09.046; PII: S0022-4596(05)00448-2; Copyright (c) 2005 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:
36 MATERIALS SCIENCE; ANIONS; ANTIFERROMAGNETISM; BARIUM COMPOUNDS; CATIONS; LAYERS; MANGANESE COMPOUNDS; NEUTRON DIFFRACTION; OXIDES; PEROVSKITE; STRONTIUM COMPOUNDS; STRUCTURAL MODELS; SYNTHESIS; VACANCIES

Citation Formats

Adkin, Josephine J., and Hayward, Michael A.. Structure and magnetism of 4H-BaMnO{sub 3-x} (0=<x=<0.35) and 4H-Ba{sub 0.5}Sr{sub 0.5}MnO{sub 3-x} (0=<x=<0.21). United States: N. p., 2006. Web. doi:10.1016/j.jssc.2005.09.046.
Adkin, Josephine J., & Hayward, Michael A.. Structure and magnetism of 4H-BaMnO{sub 3-x} (0=<x=<0.35) and 4H-Ba{sub 0.5}Sr{sub 0.5}MnO{sub 3-x} (0=<x=<0.21). United States. doi:10.1016/j.jssc.2005.09.046.
Adkin, Josephine J., and Hayward, Michael A.. Sun . "Structure and magnetism of 4H-BaMnO{sub 3-x} (0=<x=<0.35) and 4H-Ba{sub 0.5}Sr{sub 0.5}MnO{sub 3-x} (0=<x=<0.21)". United States. doi:10.1016/j.jssc.2005.09.046.
@article{osti_20784832,
title = {Structure and magnetism of 4H-BaMnO{sub 3-x} (0=<x=<0.35) and 4H-Ba{sub 0.5}Sr{sub 0.5}MnO{sub 3-x} (0=<x=<0.21)},
author = {Adkin, Josephine J. and Hayward, Michael A.},
abstractNote = {The synthesis and structure determination of 4H-BaMnO{sub 3-x} (0=<x=<0.35) and 4H-Ba{sub 0.5}Sr{sub 0.5}MnO{sub 3-x} (0=<x=<0.21) is described. Neutron powder diffraction data unambiguously show the anion vacancies in the oxygen-deficient phases lie in the hexagonal BaO{sub 3-x} layers, rather than the cubic layers predicted by previous structural models. The localization of anion vacancies in the hexagonal layers is discussed on the basis of the local co-ordination polyhedra of the metal cations. Low-temperature neutron diffraction data show the oxidized materials adopt antiferromagnetic ordered structures (Ba{sub 0.5}Sr{sub 0.5}MnO{sub 2.99}: T{sub N}=265K). Anion-deficient phases do not achieve magnetic order suggesting the Mn(III/IV) charge disorder suppresses long-range magnetic order.},
doi = {10.1016/j.jssc.2005.09.046},
journal = {Journal of Solid State Chemistry},
number = 1,
volume = 179,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2006},
month = {Sun Jan 15 00:00:00 EST 2006}
}
  • The crystal and magnetic structures of newly synthesized Sr{sub 1-x}Ca{sub x}MnO{sub 3} (0{<=}x{le}1) and Sr{sub 1-y}Ba{sub y}MnO{sub 3} (y{<=}0.2) perovskite materials (of the ABO{sub 3} type) were investigated using neutron and synchrotron x-ray powder diffraction at temperatures between 10 and 530 K. Upon decreasing the size of the A-site ion (or the unit-cell size) a series of structural transitions appears at room temperature from cubic Pm{bar 3}m to tetragonal I4/mcm (at x{approx}0.3) to orthorhombic Pbnm at x{approx}0.4. In agreement with neutron-diffraction data, resistive and magnetic measurements show that the samples are antiferromagnetic with Neel temperatures T{sub N}, varying from 233more » to {approx}125 K and from 233 to 212 K by increasing the Ca and Ba contents, respectively. The observed variation of T{sub N} cannot be solely explained by the changes of the unit-cell size or the average Mn-O-Mn bond angle {theta}. The behavior of T{sub N} can be satisfactorily described as a function of <cos{sup 2} {theta}> related to the superexchange interaction integral, and {sigma}{sup 2}, the A-site ionic size variance [L. M. Rodriguez-Martinez and J. P. Attfield, Phys. Rev. B 54, R15 622 (1996)] regardless of the structural symmetry of the perovskite material.« less
  • Structural and magnetic studies are presented for the perovskite type Sr{sub 1-x}La{sub x}Co{sub 0.5}Fe{sub 0.5}O{sub 3-{delta}} (0{<=}x{<=}0.5) materials annealed under moderately high-oxygen pressures of {approx}200 atm. A detailed analysis of the room temperature neutron time-of-flight diffraction data reveals that the crystal structure of the sample SrCo{sub 0.5}Fe{sub 0.5}O{sub 2.89(1)}, previously described as vacancy-disordered cubic, is similar to the formerly reported, oxygen-vacancy ordered Sr{sub 8}Fe{sub 8}O{sub 23} compound, i.e. Sr{sub 8}Co{sub 4}Fe{sub 4}O{sub 23} is tetragonal with the I4/mmm symmetry. With an increase of the La content the studied materials become nearly oxygen stoichiometric and a lowering of the crystal symmetrymore » is observed from cubic Pm3-barm (x=0.1 and 0.2) to tetragonal I4/mcm (x=0.3 and 0.4), and finally to monoclinic I12/c1 (x=0.5). Low-temperature structural and magnetic measurements show a ferromagnetic ordering with the maximum Curie temperature near 290 K at x=0.2. - Graphical Abstract: Room temperature Rietveld refinement profile using I4/mmm space group for the oxygen vacancy ordered SrCo{sub 0.5}Fe{sub 0.5}O{sub 2.89} (Sr{sub 8}Co{sub 4}Fe{sub 4}O{sub 23}). Top tick-marks denote allowed reflections in I4/mmm, bottom one emphasize the possibility of inexact indexing using Pm3-barm symmetry. Previous reports indicate that similar ordering is common for SrCo{sub 1-x}Fe{sub x}O{sub 3-{delta}} compounds possibly hindering their applications.« less
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