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- Bielecki, Johan, 1982, et al.
(författare)
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Structural and magnetic properties of isovalently substituted multiferroic BiFeO3 : Insights from Raman spectroscopy
- 2012
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 86:184422
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Tidskriftsartikel (refereegranskat)abstract
- Raman spectra, supplemented by powder x-ray diffraction and magnetization data of isovalently A- and B-site substituted BiFeO3 in the Bi1−xLaxFeO3 (0≤x≤1), Bi1−xTbxFeO3 (0≤x≤0.2), and Bi0.9Sm0.1Fe1−xMnxO3 (0≤x≤0.3) series, are presented. A good agreement between the structural transitions observed by x-ray diffraction and the vibrational modes observed in the Raman spectra is found over the whole substitutional ranges, and in particular we find spectroscopic signatures of a PbZrO3-type structure for Bi0.8La0.2FeO3. Mode assignments in the substituted materials are made based on Raman spectra of the end-members BiFeO3 and LaFeO3. Moreover, by comparing spectra from all samples with R3c structure, the phonon assignment in BiFeO3 is revisited. A close connection between the degree of octahedral tilt and the Raman shift of the A1 oxygen a−a−a− tilt mode is established. An explanation for the strong second-order scattering observed in Bi1−xLaxFeO3 and Bi1−xTbxFeO3 is suggested, including the assignment of the previously mysterious BiFeO3 mode at 620 cm−1. Finally, the magnetization data indicates a transition from a cycloidal modulated state towards a canted antiferromagnet with increasing A-site substitution, while Bi0.9Sm0.1Fe1−xMnxO3 with x=0 and 0.15 exhibit an anomalous closing of the hysteresis loop at low temperatures. For low A-site substitution levels (x≤0.1) the decreasing Raman intensity of the Fe derived modes correlates with the partial destruction of the spin cycloid as the substitution level increases.
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| 2. |
- Knee, Christopher, 1973, et al.
(författare)
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High Pressure Crystal and Magnetic Phase Transitions in Multiferroic Bi0.9La0.1FeO3
- 2014
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 26:2, s. 1180-1186
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Tidskriftsartikel (refereegranskat)abstract
- The crystal and magnetic structures of multiferroic Bi0.9La0.1FeO3 have been studied using high resolution neutron powder diffraction in the pressure range 0-8 GPa. Two structural phase transitions are observed. The first, at similar to 1 GPa, transforms the polar R3c structure to an antipolar PbZrO3-like root 2a(p) x 2 root 2a(p) x 2a(p) perovskite superstructure; the second, at similar to 5 GPa, results in a smaller, root 2a(p) x root 2a(p) x 2a(p) unit cell and a structure described with Ibmm (nonstandard setting of Imma) symmetry, in which the a(-)a(-)b(0) octahedral tilt system is retained and the antipolar cation displacements lost. Accompanying the changes in the nuclear structure, the antiferromagnetic spin structure evolves from a cycloid, with a modulation length, lambda approximate to 770 angstrom, to collinear arrangements with the moments aligned along the b-axis (Pbam) and the a-axis (Ibmm) of the orthorhombic unit cells. In comparison with BiFeO3 the transition from a rhombohedral to an orthorhombic structure is suppressed by similar to 3 GPa, reflecting the dilution of the stereochemically active bismuth lone pair by lanthanum. A correlation between the cell contraction of Bi1-xLaxFeO3 (0.0
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