RAMAN-SPECTROSCOPY OF ORTHORHOMBIC PEROVSKITELIKE YMNO3 AND LAMNO3

The Raman-active phonons in orthorhombic perovskite like YMnO3 and LaM nO3 were studied by measuring Raman spectra in various scattering conf igurations. The experimental Raman line wave numbers and the expected shapes for the phonon modes were compared to those reported for other perovskite like compounds with the Pnma structure and to the results o f lattice dynamical calculations. The observed Raman lines in the spec tra of YMnO3 and LaMnO3 were assigned to definite atomic motions. The much larger linewidths and strong variation of the Raman spectra with increasing laser power in the case of LaMn03 provide evidence for a st ructural instability that may result in a phase transition under laser annealing.