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Title: Local and average structure of Mn- and La-substituted BiFeO{sub 3}

Abstract

The local and average structure of solid solutions of the multiferroic perovskite BiFeO{sub 3} is investigated by synchrotron X-ray diffraction (XRD) and electron density functional theory (DFT) calculations. The average experimental structure is determined by Rietveld refinement and the local structure by total scattering data analyzed in real space with the pair distribution function (PDF) method. With equal concentrations of La on the Bi site or Mn on the Fe site, La causes larger structural distortions than Mn. Structural models based on DFT relaxed geometry give an improved fit to experimental PDFs compared to models constrained by the space group symmetry. Berry phase calculations predict a higher ferroelectric polarization than the experimental literature values, reflecting that structural disorder is not captured in either average structure space group models or DFT calculations with artificial long range order imposed by periodic boundary conditions. Only by including point defects in a supercell, here Bi vacancies, can DFT calculations reproduce the literature results on the structure and ferroelectric polarization of Mn-substituted BiFeO{sub 3}. The combination of local and average structure sensitive experimental methods with DFT calculations is useful for illuminating the structure-property-composition relationships in complex functional oxides with local structural distortions. - Graphical abstract:more » The experimental and simulated partial pair distribution functions (PDF) for BiFeO{sub 3}, BiFe{sub 0.875}Mn{sub 0.125}O{sub 3}, BiFe{sub 0.75}Mn{sub 0.25}O{sub 3} and Bi{sub 0.9}La{sub 0.1}FeO{sub 3}.« less

Authors:
;
Publication Date:
OSTI Identifier:
22658290
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 250; Other Information: Copyright (c) 2017 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; BISMUTH COMPOUNDS; COMPUTER CALCULATIONS; DENSITY FUNCTIONAL METHOD; DISTRIBUTION FUNCTIONS; ELECTRON DENSITY; EXPERIMENTAL DATA; FERRITES; FERROELECTRIC MATERIALS; MANGANESE COMPOUNDS; OXIDES; SIMULATION; SOLID SOLUTIONS; SPACE GROUPS; STRUCTURAL MODELS; X-RAY DIFFRACTION

Citation Formats

Jiang, Bo, and Selbach, Sverre M., E-mail: selbach@ntnu.no. Local and average structure of Mn- and La-substituted BiFeO{sub 3}. United States: N. p., 2017. Web. doi:10.1016/J.JSSC.2017.03.021.
Jiang, Bo, & Selbach, Sverre M., E-mail: selbach@ntnu.no. Local and average structure of Mn- and La-substituted BiFeO{sub 3}. United States. doi:10.1016/J.JSSC.2017.03.021.
Jiang, Bo, and Selbach, Sverre M., E-mail: selbach@ntnu.no. Thu . "Local and average structure of Mn- and La-substituted BiFeO{sub 3}". United States. doi:10.1016/J.JSSC.2017.03.021.
@article{osti_22658290,
title = {Local and average structure of Mn- and La-substituted BiFeO{sub 3}},
author = {Jiang, Bo and Selbach, Sverre M., E-mail: selbach@ntnu.no},
abstractNote = {The local and average structure of solid solutions of the multiferroic perovskite BiFeO{sub 3} is investigated by synchrotron X-ray diffraction (XRD) and electron density functional theory (DFT) calculations. The average experimental structure is determined by Rietveld refinement and the local structure by total scattering data analyzed in real space with the pair distribution function (PDF) method. With equal concentrations of La on the Bi site or Mn on the Fe site, La causes larger structural distortions than Mn. Structural models based on DFT relaxed geometry give an improved fit to experimental PDFs compared to models constrained by the space group symmetry. Berry phase calculations predict a higher ferroelectric polarization than the experimental literature values, reflecting that structural disorder is not captured in either average structure space group models or DFT calculations with artificial long range order imposed by periodic boundary conditions. Only by including point defects in a supercell, here Bi vacancies, can DFT calculations reproduce the literature results on the structure and ferroelectric polarization of Mn-substituted BiFeO{sub 3}. The combination of local and average structure sensitive experimental methods with DFT calculations is useful for illuminating the structure-property-composition relationships in complex functional oxides with local structural distortions. - Graphical abstract: The experimental and simulated partial pair distribution functions (PDF) for BiFeO{sub 3}, BiFe{sub 0.875}Mn{sub 0.125}O{sub 3}, BiFe{sub 0.75}Mn{sub 0.25}O{sub 3} and Bi{sub 0.9}La{sub 0.1}FeO{sub 3}.},
doi = {10.1016/J.JSSC.2017.03.021},
journal = {Journal of Solid State Chemistry},
number = ,
volume = 250,
place = {United States},
year = {Thu Jun 15 00:00:00 EDT 2017},
month = {Thu Jun 15 00:00:00 EDT 2017}
}
  • The local and average structure of solid solutions of the multiferroic perovskite BiFeO 3 is investigated by synchrotron X-ray diffraction (XRD) and electron density functional theory (DFT) calculations. The average experimental structure is determined by Rietveld refinement and the local structure by total scattering data analyzed in real space with the pair distribution function (PDF) method. With equal concentrations of La on the Bi site or Mn on the Fe site, La causes larger structural distortions than Mn. Structural models based on DFT relaxed geometry give an improved fit to experimental PDFs compared to models constrained by the space groupmore » symmetry. Berry phase calculations predict a higher ferroelectric polarization than the experimental literature values, reflecting that structural disorder is not captured in either average structure space group models or DFT calculations with artificial long range order imposed by periodic boundary conditions. Only by including point defects in a supercell, here Bi vacancies, can DFT calculations reproduce the literature results on the structure and ferroelectric polarization of Mn-substituted BiFeO 3. The combination of local and average structure sensitive experimental methods with DFT calculations is useful for illuminating the structure-property-composition relationships in complex functional oxides with local structural distortions.« less
  • We used neutron powder diffraction to obtain the local and long-range structure of La{sub 0.5}Ca{sub 0.5}MnO{sub 3} at room temperature and 20 K. By combining Rietveld and pair distribution function analysis of the total neutron scattering data, we have analyzed the structure of the compound using two competing models describing the low temperature phase: first the charge-ordered-orbital-ordered model and second the Mn-Mn dimer model. These structural models fit the 20 K neutron powder diffraction pattern equally well using a Rietveld analysis. Therefore, pair distribution function analysis is used to probe the local and medium-range structure revealing a system with twomore » distinctly distorted Mn octahedra and Mn ions with nonintegral valence states. The distorted octahedra differ with the structural model for the Zener polaron-type Mn-Mn dimer picture proposed for Pr{sub 0.60}Ca{sub 0.40}MnO{sub 3} and order in a similar checkerboard configuration associated with the CE-type antiferromagnetic structure. Therefore, locally the charge difference and structural ordering between the two Mn is appreciable enough to describe the system at 20 K as ''partially charge ordered.''.« less
  • Polycrystalline samples of pure BiFeO{sub 3}-PbTiO{sub 3} (BF-PT) and those upon substituting Bi by La up to 50% (x{<=}0.5) were synthesized using a solid-state reaction method. A composition-driven tetragonal-cubic transition, identified from X-ray diffraction, was found to occur at x=0.4. We report the phonon spectra of pure and La-substituted BF-PT and its assignment. From the behavior of total Raman intensity, the origin of the symmetry-forbidden Raman spectra is identified to lie in substitutional disorder. The dependence of splitting of A{sub 1}-E modes and that of the LO-TO modes on composition are obtained and their consequences on ionicity are discussed. -more » Graphical abstract: Raman spectrum of the cubic phase (x{>=}0.4) of La-substituted BF-PT [0.5(Bi{sub 1-x}La{sub x}FeO{sub 3})0.5(PbTiO{sub 3})] consists of 7 modes, while group theory does not predict any Raman active phonon. Highlights: > Composition-driven tetragonal-cubic transition in La-substituted BF-PT. > Phonon spectra in the tetragonal phase assigned. > A{sub 1}-E anisotropy splitting of phonons decreases upon La-substitution. > Increase in LO-TO splitting at larger La composition due to higher ionicity.« less
  • BiFeO{sub 3} (BFO) and La{sub x}Sr{sub y}Mn{sub z}O{sub 3} (LSMO) films were epitaxially grown on SrTiO{sub 3} (100) substrates by r.f. magnetron sputtering with various oxygen gas flow ratios (F{sub O2}). Compositional ratios of each atom in both of BFO and LSMO could be controlled kept to around 10 at.% by changing F{sub O2}. Adjusting the compositional ratio to La{sub 0.35}Sr{sub 0.15}Mn{sub 0.5}O{sub 3} not only increase T{sub c} of LSMO but also produces sufficient oxygen to form a perovskite lattice. For an LSMO/BFO heterostructure, detailed observation by cross sectional transmission electron microscopy (TEM) revealed that the lattice of rhombohedralmore » (SG: R-3c) LSMO was shrank by a clamping effect from the SrTiO{sub 3} substrates, and then the BFO was grown in two layers: (i) an interfacial BFO layer (7 nm thick) with evenly shrunk a-axis and c-axis, and (ii) an upper BFO layer (25 nm thick) expanded along the c-axis. Neither misfit strain nor dislocations appeared at the interface between the shrunken BFO and LSMO layers, and these heterostructures did not show exchange bias. These results suggest that BFO is suitable for a tunneling barrier combine with LSMO electrode.« less