Raman spectroscopy of low-temperature(Pnma)and high-temperature(R3¯c

We present the polarized Raman spectra of $\mathrm{La}\mathrm{Cr}{\mathrm{O}}_{3}$ measured between 5 and $863\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in several exact scattering configurations. All Raman lines below $600\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ are assigned to definite phonon modes of $Pnma$ $(\mathrm{T}<528\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ or $R\overline{3}c$ $(\mathrm{T}>528\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ structures on the basis of their polarization properties, comparison to spectra of isostructural compounds, and comparison to mode frequencies predicted by calculations of lattice dynamics. The broad overlapping high-frequency bands between 600 and $750\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ of ${A}_{g}$ character, which are sample dependent and vary significantly upon annealing in vacuum or change of excitation photon energy, are assigned to local vibrations of ${\mathrm{Cr}}^{4+}$-related defect species. These results can serve as a ground for further study of microstructure-property relationships in practically important doped rare earth chromates.