RAMAN-SCATTERING IN LA1-XSRXMNO3 SINGLE-CRYSTALS (X = 0, 0.1, 0.2, 0.3)

We report polarized Raman spectra of La1-xSrxMnO3 crystals (x = 0, 0.1 , 0.2 and 0.3) in the temperature range from 5 K to 300 K. The small d istortion of the nearly cubic lattice of doped La1-xSrxMnO3 single cry stals results in a structured phonon Raman spectrum which is composed of two parts with different contributions depending on the value of do ping. The first part is assigned to the distorted non-cubic perovskite lattice and follows the selection rules for a tetragonal structure. T his suggests the possible presence of a tetragonal structure in doped La1-xSrxMnO3 single crystals. The second part is mainly due to the den sity of vibrational states and is attributed to the second-order Raman scattering. The frequency of the A(1g)-like mode was found to be sens itive to doping but the observed shift is opposite to that expected fr om the difference in the atomic weight of Sr and La. This mode exhibit s also an anomalously large shift of similar to 20 cm(-1) in the tempe rature range from 5 K to 300 K. A possible explanation of this behavio ur is suggested. (C) 1998 Elsevier Science Ltd.