POLARIZED INFRARED REFLECTANCE SPECTRA OF SINGLE-CRYSTAL ALPHA-BI2O3

Polarized IR reflectance spectra of monoclinic single crystal alpha-Bi 2O3 for different directions of the wave vector k and the electric fie ld E of the incident radiation have been measured in a wide temperatur e range (25-400 K). A significant dependence of the spectrum shape on the direction of the vector E within the ac-plane was observed. Freque ncies, strengths, widths and polarizations of the TO modes were restor ed using the Lorentz dispersion model extended for the monoclinic crys tal lattice. Remarkable distinction between intensities of A(u)- and B -u-modes is observed.