LATTICE AND STRUCTURAL DISTORTIONS IN Gd3+ SUBSTITUTED LaMnO3: INFRARED REFLECTIVITY MEASUREMENTS

Polycrystalline La1-xGdxMnO3 multiferroics (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) have been successfully synthesized by sol-gel combustion method. Rietveld refinement of X-ray diffraction (XRD) patterns clearly demonstrates a structural distortion from orthorhombic to rhombohedral perovskite-type structure, which suggests strong Jahn-Teller distortion. The infrared reflectivity (IR) spectra are measured at room temperature over a frequency range 30-7500 cm(-1) by Fourier transform infrared (FTIR) spectrometer which exhibits several optical phonons. The resonant frequency (omega(TO(j))), oscillator strength (S-j) and damping factor (gamma(j)) of various observed optical phonons have been determined by fitting the Lorentz oscillator model to the measured reflectivity spectra. The iii Too) is found dependent on Gd concentration suggesting a strong electron-phonons interaction in the system. The optical conductivity sigma(1) (omega) calculated by using the Kramers-Kroning analysis of the IR spectra also confirms the phase transition on increasing the Gd concentration. The Born effective charges have been calculated using the transverse (TO) and longitudinal optical (LO) modes to understand the role of ionic polarization in the present multiferroic system.