Franck-Condon higher order lattice excitations in the La⁢Fe1−⁢Cr⁢O3 (=0, 0.1, 0.5, 0.9, 1.0) perovskites due to Fe-Cr charge transfer effects

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Erscheinungsjahr:
2007
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  • First and higher order lattice excitations in the -site disordered perovskites La⁢Fe1−⁢Cr⁢O3 (=0, 0.1, 0.5, 0.9, and 1) and La0.835⁢Sr0.165⁢Fe0.5⁢Cr0.5⁢O3− are investigated using temperature dependent and polarized inelastic light scattering [=515nm (2.41eV) and 676nm (1.83eV)] on oriented crystallites. A peak at approximately 2.4eV in the imaginary part of the dielectric function of La⁢Fe0.5⁢Cr0.5⁢O3 is assigned to a charge transfer from Fe3+ (5) to Cr3+ (3) ions, coupled with the appearance of an intense -like mode at approximately 700cm−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 La⁢Ma⁢O3. 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 La⁢Fe1−⁢Cr⁢O3 system as a model system for electron-phonon coupling and higher order Raman scattering in solids.
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  • info:eu-repo/semantics/closedAccess
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Forschungsinformationssystem der UHH

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