Phonon Raman scattering in R1-xAxMnO3+δ (R = La,Pr; A = Ca,Sr)

Polarized Raman spectra of single and polycrystalline R(1-x)A(x)MnO(3) (R = La,Pr;A = Ca,Sr) ceramic samples were studied as a function of temperature. For the rhombohedral LaMnO3.1 and La0.7Sr0.3MnO3, the observed Raman peaks were associated with modes arising from the folding of the Brillouin zone under lattice deformation. For the orthorhombic LaMnO3.0, the Raman spectra are consistent with the Pnma structure and show an anomalous softening of the 494 and 604 cm(-1) modes below the antiferromagnetic ordering temperature T-N similar or equal to 140 K. Polycrystalline samples of La0.5Ca0.5MnO3 show a dramatic change of the Raman spectra between 100 and 160 K, which was associated with the increase of the orthorhombic distortion observed by others for T less than or similar to 240 K. Other R(1-x)A(x)MnO(3) single crystals, with small orthorhombic distortions, show Raman spectra which are similar to those observed in the rhombohedral samples. [S0163-1829(98)05338-7].