Ceramics-Silikáty 56, (2) 95 - 101 (2012)

Using spectroscopic ellipsometry, we have studied the optical properties of doped manganites at the paramagnetic state in polycrystalline La_0.7Ca_0.3-xK_xMnO₃ samples for (x = 0.00, 0.05 and 0.10) in the energy range of 3.2-5.5 eV at room temperature. The surface morphology of the samples was obtained by using atomic force microscopy (AFM). Refractive indices, extinction coefficients, the transmission ellipsometric parameters Ψ and Δ are investigated at different wavelengths. The study of the optical conductivity σ reveals that optical behaviour and the activated transport in the paramagnetic state of these materials are consistent with Jahn-Teller small polaron. In addition, the spectrum of the complex dielectric constant ε reveals peaks for all samples, the results may be explained by the presence of space charges from the strongly dipole-allowed O(2p)−Mn(3d) transition.