The Raman and infrared phonons of isostructural rhombohedral LaMnO 3 and LaAlO 3 are studied at room temperature. The experimental spectra are compared with the prediction of lattice-dynamical calculations and the lines observed are assigned to definite atomic vibrations. It is shown that the Raman mode of A 1g symmetry in LaAlO 3 and LaMnO 3 ͑at 123 cm Ϫ1 and 236 cm Ϫ1 , respectively͒ involves atomic motions that cause the rhombohedral distortion, i.e., it is a ''soft'' mode, and its position could be used as a measure of the degree of the distortion. It is also argued that the broad Raman bands in the high-frequency range of LaMnO 3 are not proper modes of the rhombohedral R3 c structure, but are rather induced by the dynamic Jahn-Teller effect.

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The Raman spectra of single crystals of NiFe2O4 were studied in various scattering configurations in close comparison with the corresponding spectra of Ni0.7Zn0.3Fe2O4 and Fe3O4. The number of experimentally observed Raman modes exceeds significantly that expected for a normal spinel structure and the polarization properties of most of the Raman lines provide evidence for a microscopic symmetry lower than that given by the F d3m space group. We argue that the experimental results can be explained by considering the short range 1:1 ordering of Ni 2+ and Fe 3+ at the B-sites of inverse spinel structure, most probably of tetragonal P 4122/P 4322 symmetry.

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