Infrared Active Phonons and Optical Band Gap in Multiferroic GdMnO3Studied by Infrared and UV-Visible Spectroscopy

Optical properties of multiferroic GdMnO3 synthesized by sol-gel method have been investigated by measuring the infrared reflectivity and UV-visible absorption spectra.The infrared reflectivity spectrum of polycrystalline GdMnO3 in the frequency range 30-7500 cm -1 at room temperature contains several phonon modes.The resonant frequency of observed infrared active phonon modes is found comparable with theoretically predicted results.Mean Born effective charges are calculated and discussed in view of the origin of ferroelectricity in GdMnO3.Three strong absorption peaks observed in the UV-visible spectrum are attributed to the Mn (3d)-electron transitions.The optical band gap ≈ 1.2 eV is estimated from UV-visible absorption spectrum using Tauc's relation.GdMnO3 seems to behave like an indirect gap semiconductor.