Infrared reflectivity of the solid solutions LaNi{sub 1{minus}x}Fe{sub x}O{sub 3} (0.00{le}x{le}1.00)
- Laboratorio Nacional de Investigacion y Servicios en Espectroscopia Optica, Centro CEQUINOR, Departamento de Quimica y Departamento de Fisica, Universidad Nacional de La Plata, Casilla de Correo 962, 1900 La Plata (Argentina)
- Instituto de Investigaciones en Fisicoquimica de Cordoba, Departamento de Fisicoquimica, Facultad de Ciencias Quimicas, Universidad Nacional de Cordoba, Agencia Postal 4, Casilla de Correo 61, 5000 Cordoba (Argentina)
- Laboratorio de Resonancias Magneticas, Centro Atomico Bariloche, 8400 Bariloche, Rio Negro (Argentina)
We report temperature-dependent far- and midinfrared reflectivity spectra of LaNi{sub (1{minus}x)}Fe{sub x}O{sub 3} solid solutions that span the passage from LaFeO{sub 3}, a room-temperature antiferromagnetic insulator, to LaNiO{sub 3}, a known metal oxide. Light Ni doping creates defects that induce extra bands assigned to electronic transitions within the insulating gap. An incipient Drude term emerges in the reflectivity spectrum of LaNi{sub 0.39}Fe{sub 0.61}O{sub 3} together with subbands that contribute to the electronic background. At these concentrations the dielectric response shows a picture in which the spectral weigh switches over toward far-infrared frequencies while phonon features develop strong antiresonances near longitudinal-optical modes. Further increment of carriers produces phonon screening and the development of a reflectivity tail that extends beyond 1 eV. We assign extra-non-Drude terms in the 700{endash}4000cm{sup {minus}1} frequency region to transitions due to intrinsic defects. While the increment in reflectivity at far-infrared frequencies is evident for Fe concentrations well above the insulator-metal transition (x{approximately}0.30), the spectral features of a metal oxide, with phonons mostly screened, are found for x=0.23. These metallic spectra show an absorption dip at {approximately}650cm{sup {minus}1} that is traced to the perovskite symmetric stretching longitudinal mode. Electron-phonon interactions are thus present in solid solutions even when the numbers of effective carriers are those of a metal. This characterization is also supported by the observation of weak reflectivity dips in LaNiO{sub 3} that have a direct correspondence to longitudinal-optical mode frequencies of the insulating phases of our series. We infer that strong electron-phonon interactions play a role in the conductivity of those solid solutions and are likely related to polaron formation and carrier phonon-assisted hopping motion. (Abstract Truncated)
- OSTI ID:
- 550385
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 56, Issue 16; Other Information: PBD: Oct 1997
- Country of Publication:
- United States
- Language:
- English
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