The Raman-active phonons in orthorhombic perovskitelike ${\mathrm{YMnO}}_3$ and ${\mathrm{LaMnO}}_3$ were studied by measuring Raman spectra in various scattering configurations. The experimental Raman line wave numbers and the expected shapes for the phonon modes were compared to those reported for other perovskitelike compounds with the $\mathrm{Pnma}$ structure and to the results of lattice dynamical calculations. The observed Raman lines in the spectra of ${\mathrm{YMnO}}_3$ and ${\mathrm{LaMnO}}_3$ 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 ${\mathrm{LaMnO}}_3$ provide evidence for a structural instability that may result in a phase transition under laser annealing.

The Raman and infrared phonons of isostructural rhombohedral ${\mathrm{LaMnO}}_3$ and ${\mathrm{LaAlO}}_3$ 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 ${\mathrm{LaAlO}}_3$ and ${\mathrm{LaMnO}}_3$ (at $123\hspace{0.5em}{\mathrm{cm}}^{-1}$ and $236\hspace{0.5em}{\mathrm{cm}}^{-1},$ respectively) 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 ${\mathrm{LaMnO}}_3$ are not proper modes of the rhombohedral $R3\mathrm{}¯c$ structure, but are rather induced by the dynamic Jahn-Teller effect.

The polarized Raman spectra of orthorhombic $R{\mathrm{MnO}}_3$ series $(R=\mathrm{La},\mathrm{Pr},\mathrm{Nd},\mathrm{Sm},\mathrm{Eu},\mathrm{Gd},\mathrm{Tb},\mathrm{Dy},\mathrm{Ho},\mathrm{Y})$ were studied at room temperature. The variation of phonon frequencies with $R$ ionic radius $r_R$ as a whole confirms the commonly accepted Raman line assignments with two noticeable exceptions: (1) with decreasing $r_R$ the stretching $A_g\left(1\right)$ and bending $A_g\left(3\right)$ modes strongly mix for $R=\mathrm{Sm}$ to Tb, while for further decrease or $r_R$ $(R=\mathrm{Dy},\mathrm{Ho},\mathrm{Y})$ the $A_g\left(3\right)$ mode is observed at higher frequency than $A_g\left(1\right)$ mode; (2) similar distortion-dependent mode mixing takes place for the rotational $A_g\left(2\right)$ and $\mathrm{O}1\left(x\right)$ $\left[A_g\right(7\left)\right]$ modes. The mode mixing is particularly strong for the $R{\mathrm{MnO}}_3$ compounds with $r_R$ values close to the transition from $A$ type to incommensurate sinusoidal antiferromagnetic ordering at low temperatures. The frequency of rotational $A_g\left(2\right)$ and $A_g\left(4\right)$ modes scales to the angles of ${\mathrm{MnO}}_6$ $\left[101\right]$ and $\left[010\right]$ rotations, respectively, and could be used as a measure of their value.

The Raman spectra of epitaxial thin films of ${\mathrm{La}}_2\mathrm{Co}\mathrm{Mn}{\mathrm{O}}_6$ on (001)-oriented $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ substrates have been measured in several exact scattering configuration between 12 and $890\mathrm{K}$. The polarization dependence of the spectra provide clear evidence for ordered $P{12}_1∕n1$ structure, differing from its parent $Fm\overline{3}m$ structure by the presence of rotational distortions. The correlation between the phonon modes in $Fm\overline{3}m$, $R\overline{3}$, and $P{12}_1∕n1$ phases is analyzed and the corresponding types of atomic motions as well as their expected frequency range are determined by comparison to the predictions of lattice dynamical calculations. The ferromagnetic ordering and spin-phonon coupling below $T_C$ result in softening of some of the phonon modes. The evolution of the Raman spectra at high temperatures shows no indication for $P{12}_1∕n1–R\overline{3}$ transition up to $800\mathrm{K}$.

Raman-scattering and far-infrared-transmission spectra of hexagonal ${\mathrm{YMnO}}_3$ (space group ${P6\mathrm{}}_{3}cm)$ are reported and discussed. In the Raman spectra measured in several exact scattering configurations, lines of $A_1$ (at 148, 190, 257, $\sim 300$, 433, 459, and 681 cm${}^{-1})$, $E_1$ (at 376, 408, and 632 cm${}^{-1})$, and $E_2$ (at 135, and $\sim 215$ cm${}^{-1})$, symmetries have been observed. Maxima in the infrared absorption have been found at 211, 238, 265, 281, 308, 398, 428, 457, 491, 596, and 612 cm${}^{-1}$. An assignment of the phonon lines to definite atomic vibrations has been made on the basis of their symmetries in close comparison with results of lattice-dynamical calculations for ${\mathrm{YMnO}}_3$ in its ferroelectric ${(P6\mathrm{}}_{3}cm,\hspace{0.5em}Z=6)$ and high-temperature paraelectric ${(P6\mathrm{}}_3/mmc,\hspace{0.5em}Z=2)$ phases.