The paper presents a polarized Raman scattering study of a few-micron-size crystallite of LiBC with natural faces. The experiment on an as grown sample revealed four lattice modes with frequencies at 1176, 830, 546, and 170 ${\mathrm{cm}}^{-1},$ respectively. The number of observed Raman lines and their selection rules are incompatible with the assumed ${\mathrm{D}}_{6\mathrm{h}}$ symmetry. The modes at 1176 and $170{\mathrm{cm}}^{-1}$ correspond to the expected Raman active modes. In contrast to the superconducting compound ${\mathrm{MgB}}_2,$ the B-C bond stretching mode (at $1176{\mathrm{cm}}^{-1})$ has rather small damping. The two “forbidden” modes (at 830 and $546{\mathrm{cm}}^{-1})$ disappeared after a subsequent thermal treatment.

• Received 27 September 2002

DOI:https://doi.org/10.1103/PhysRevB.67.020504