Doping and oxidation effects in raman spectra of manganites

Roman scattering from La_yR_xMnO_3-δ compounds (single crystals, ceramics, films) was studied as a function of kind (R) and amount (x) of dopant as well as of oxygen deficit (δ). For x = 0.1 to 0.55, a nearly linear Raman shift of the A_g mode from 240 to 125 cm^-1 was observed in Sr-doped compounds. While the intensity of disorder-induced Raman bands was found to be sensitive to the oxygen content, the symmetry allowed related Raman modes exhibit the changes in the frequency. As an indication of deposition conditions, lowering of a symmetry of the film structures with respect to single crystals and ceramics was detected. We discuss the physical nature of the observed effects and show how Raman data can be used for the optical characterization of manganite samples.