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

Optical investigations of La_0.7Ca_0.3-xK_xMnO₃ (x = 0.00, 0.05 and 0.10) probed by spectroscopic ellipsometry

N. Sdiri, A. Boukhachem, E. Dhahri

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.

Keywords: K doped manganites, Spectroscopic ellipsometry, Complex index, Dispersion, Phase transition