Raman spectroscopy of multiferroic trigonal boracite Co3 B7 O13 Cl

Raman microscopy was applied to study the polarized Raman scattering from untwinned domains of Co3 B7 O13 Cl (Co-Cl) in the trigonal, R3c, ferroelectric phase. The symmetry (A1 or E) and mode polarization (LO or TO) for all observed Raman lines were determined from comparison of the spectra measured in several scattering configurations. It was found that as a rule, the TO-LO splitting is small or negligible. A group of A1 modes, characterized by a quasi-one-component Raman tensor, was tentatively assigned to stretching vibrations of Cl, O, or B along the trigonal axis, which in this material is parallel to the ferroelectric polarization direction. © 2007 The American Physical Society.