Raman scattering study of perovskite manganites

Raman spectroscopy is shown to be a useful tool for the study of phase transitions, oxygen disorder and local vibrational modes in lanthanum manganese compounds of the perovskite type. In this work, we present results of the Raman scattering and x-ray diffraction studies of La0.7Sr0.3Mn1-xMxO3 manganites (M=Fe, Co, Ni, Cr). A part of Mn atoms was substituted by M with x in the range of 0.0–0.60. Raman spectra of the La0.7Sr0.3Mn1-xMxO3 exhibit a significant dependence on the amount and kind of the dopant M, and they are sensitive to the structure and transitions driven by both doping and temperature. X-ray diffraction (XRD) analysis of these samples indicates a change in the cell parameters vs. doping content. Our main focus is the Raman peak at high frequency (>630 cm−1), that is somewhat controversial. The Raman spectra exhibit an additional high frequency mode attributed to the local breathing vibration of oxygen surrounding the substituent ion. The frequency and intensity of Raman spectra in these manganites is very sensitive to the type and content of substituent. From above results, a critical content of substituent at which the structural phase changed was shown.