Raman spectra of pure and Mn-doped Bi4Ge3O12 crystals are measured and the
observed peaks are assigned through calculating the vibrational modes of di
fferent clusters representative for the Bi4Ge3O12 structure. The doping wit
h Mn affects only the polar modes and the resulting changes in the spectra
can be explained by anisotropic embedding of Mn into the host lattice of Bi
4Ge3O12 which leads to an increase in the anisotropy of the long-range inte
ratomic interactions. (C) 1999 Elsevier Science Ltd. All rights reserved.