Raman study of phonons in Sr3Mn2O6.54 and Sr3Mn2O7 layered manganites

Polycrystalline Sr3Mn2O6.54 and Sr3Mn2O7 layered manganites were studied at room temperature using Raman spectroscopy. While the phonon spectrum of th e stoichiometric Sr3Mn2O7 sample is consistent with the group theoretical a nalysis for the I4/min structure, three additional modes are observed in th e phonon spectrum of the oxygen-deficient Sr3Mn2O6.54 sample. Based on an a nalysis of the temperature dependence of the Raman spectrum of Sr3Mn2O6.54. and a comparison with the Raman spectrum of LaSr2Mn2O7, we conclude that t he 'extra' modes should be viewed as disorder-induced Raman scattering. (C) 2001 Elsevier Science B.V. All rights reserved.