Raman phonons in orthorhombic manganites

We have investigated the Raman phonons of several series of manganites: Lax MnyO3, La1-xCaxMnO3, RMnO3 (R = rare earth) with the (Pbmn) orthorhombic st ructure. Raman spectra of non-doped samples, RMnO3, correspond quite well w ith group theory analysis predictions but present anomalies in the width an d intensity of several modes. The spectra of Ca-doped and non-stoichiometri c samples are explained taking into account structural effects (both the di sorder induced by doping and the reduction of the mean orthorhombic distort ion) and the coupling of the phonons to the more or less delocalized e(g) e lectrons, related to polarons. (C) 1999 Elsevier Science B.V. All rights re served.