RAMAN-SPECTRA AND LATTICE-DYNAMICS OF SINGLE-CRYSTAL ALPHA-BI2O3

Polarized Raman spectra of oriented monoclinic single crystals of alph a-Bi2O3 have been obtained at temperatures of 20-650 K in the region 1 5-3500 cm(-1). The assignment of the Raman bands to the A(g) and B-g m odes was given. The photoinduced reduction of the Raman intensity was observed after heating a crystal above 500 K, and cooling it down to r oom temperature, under laser irradiation. A lattice dynamical analysis based on two-particle interatomic potentials and a rigid-ion model wa s performed. These potentials were consistent with the Raman and IR da ta, besides which they showed a stable dynamics throughout the Brillou in zone, and yielded the minimum of internal forces and pressures in t he crystal lattice. The phonon dispersion curves, and the projected an d total densities of phonon states were calculated.