Far Infrared Reflectivity and Raman Scattering of Tl2?xBixMn2O7 (x = 0.00, 0.10, 0.50)

N.E. MASSA ; R.G. PREGLIASCO; A. FAINSTEIN; H. SALVA; J.A. ALONSO; M.J. MARTÍNEZ-LOPE; M. T. CASAIS.

PHYSICA STATUS SOLIDI B-BASIC RESEARCH

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2000 vol. 220 p. 373 - 376

0370-1972

We report temperature dependent infrared and Raman spectra of pyrochlores Tl2?xBixMn2O7 (x = 0.00, 0.10, 0.50). When Tl is substituted by Bi the magnetoresistance increases dramatically. This shows up in our reflectivity spectra for x = 0.10 as a weaker Drude contribution implying a downscaling of the number of active carriers at the insulator?metal phase transition (TIM) and lower temperatures. A system magnetically frustrated with no defined Tc is found for nominal x = 0.50. While in this last case the overall infrared features are maintained there is a weakening and broadening in the bands centered at ≈250 cm?1. A relative increase in intensity of the band at ≈900 cm?1, assigned to lattice polarons, is understood as indicative of stronger localization. Raman spectra are characterized by phonon bands sensitive to the bismuth content and for a band at ≈816 cm?1 that weakens when approaching TIM. We tentatively associate its origin to a bound state due to a polaron related octahedral distortion