| 1. |
- Andreasson, Jakob, et al.
(författare)
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Electron-lattice interactions in the perovskite LaFe0.5Cr0.5O3 characterized by optical spectroscopy and LDA plus U calculations
- 2009
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Ingår i: PHYSICAL REVIEW B. ; 80:7
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Tidskriftsartikel (refereegranskat)abstract
- We use resonance Raman scattering (incident photon energies between 1.8 and 4.13 eV), LDA+U calculations, spectroscopic ellipsometry, and oblique IR reflectivity to characterize the strong electron-phonon interactions in the disordered perovskite LaFe0.5Cr0.5O3. When the photon energy coincides with a Cr to Fe Mott-Hubbard transfer gap around 2.4 eV the electron-phonon interaction is manifested by a Franck-Condon effect with exceptional first-and higher order scattering of a local oxygen breathing mode. At higher incident energies we observe a superposition of Franck-Condon scattering and Frohlich interaction induced infrared active longitudinal optical two-phonon scattering activated mainly by O to Fe charge transfer. Our results establish LaFe0.5Cr0.5O3 as a model compound for research on electron-phonon interactions in strongly correlated complex systems and show that Franck-Condon scattering in complex solids is not limited to Jahn-Teller active compounds.
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| 2. |
- Andreasson, Jakob, et al.
(författare)
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Franck-Condon higher order lattice excitations in the LaFe(1-x)Cr(x)O3 (x=0, 0.1, 0.5, 0.9, 1.0) perovskites due to Fe-Cr charge transfer effects
- 2007
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Ingår i: Physical Review B. ; 75
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Tidskriftsartikel (refereegranskat)abstract
- First and higher order lattice excitations in the B-site disordered perovskites LaFe1-xCrxO3 (x=0, 0.1, 0.5, 0.9, and 1) and La0.835Sr0.165Fe0.5Cr0.5O3-delta are investigated using temperature dependent and polarized inelastic light scattering [lambda=515 nm (2.41 eV) and 676 nm (1.83 eV)] on oriented crystallites. A peak at approximately 2.4 eV in the imaginary part of the dielectric function of LaFe0.5Cr0.5O3 is assigned to a charge transfer from Fe3+ (d(5)) to Cr3+ (d(3)) ions, coupled with the appearance of an intense A(g)-like mode at approximately 700 cm(-1) in the Raman data. This excitation is identified as a symmetric oxygen breathing mode activated by the Fe-Cr charge transfer through an orbital coupling mechanism. Higher order scattering (up to seventh order) of the intrinsic Raman active symmetric breathing mode is also explained by an orbital-mediated electron-phonon coupling, similar to the Franck-Condon effect observed in the Jahn-Teller active-perovskite-structured manganite LaMaO(3). These results show that the Franck-Condon mechanism is a more common mechanism for resonant higher order scattering in solids than previously believed and propose the LaFe1-xCrxO3 system as a model system for electron-phonon coupling and higher order Raman scattering in solids.
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| 3. |
- Eriksson, Annika K., et al.
(författare)
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Influence of iron addition on the oxygen-deficient Sr0.85Bi0.15Co1-xFexO3-delta (0.0 <= x <= 1.0) perovskites
- 2008
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Ingår i: Journal of Solid State Chemistry. - 0022-4596. ; 181:8, s. 2031-2040
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Tidskriftsartikel (refereegranskat)abstract
- A series of oxygen-deficient Sr0.85Bi0.15Co1-xFexO3-delta (0.0 <= x <= 1.0) perovskite phases were prepared using solid-state reaction. Results of neutron powder diffraction analyses show that the introduction of Fe onto the B-site severely effects the long range coherence of the oxygen vacancy ordered, 14/mmm supercell, observed for the x = 0.0 sample. For x = 0.1 a smaller, a = b approximate to a(p), c approximate to 2a(p), P4/mmm supercell gives the best agreement to the diffraction data, whilst phases in the range 0.2 <= x <= 0.6 adopt disordered cubic perovskite structures. Pseudo-cubic, a = b approximate to a(p), c approximate to a(p), structures are found for x >= 0.8. Evidence of weak superstructures, reflecting local oxygen ordering, is also obtained from electron diffraction. For all oxygen-annealed phases the average structure reverts to cubic Pm (3) over barm. The as-prepared samples show G-type antiferromagnetic order at room temperature. The oxygen annealed x = 0.10, 0.25 and 1.0 samples display low-temperature spin-glass transitions.
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| 4. |
- Ivanov, S.A., et al.
(författare)
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Nuclear and Magnetic Structure of Ba3Fe2WO9
- 2004
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Ingår i: Materials Research Bulletin. ; 39, s. 615-628
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Tidskriftsartikel (refereegranskat)abstract
- The complex perovskite with composition Ba3Fe2WO9 (BFWO) has been synthesised, and the evolution of nuclear and magnetic structures with temperature has been investigated by neutron powder diffraction. It was shown that at room temperature this compound adopts the 6H-perovskite structure, space group P63/mmc (a=5.7584(2) Å, c=14.1019(9) Å), in which the cation sites within the face-sharing octahedra are occupied by Fe and W cations and those within the corner-sharing octahedra are occupied by Fe exclusively. The magnetic diffraction peaks were registered at low temperatures and a possible model for the magnetic structure was proposed in accordance with the ferrimagnetic properties of BFWO. The magnetic structure can be described as an array of ferromagnetic layers of Fe moments along the c-axis, and adjacent layers coupled antiferromagnetically. Structural and magnetic features of this compound are discussed and compared with those of other quaternary oxides adopting the 6H-perovskite structure.
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| 5. |
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