| Abstrakt: |
The far-infrared reflectivity spectroscopy with a normal and oblique (45°) light incidence has been performed with the spectra of CaCu3Ti4O12/SrRuO3/LaAlO3 (CCTO/SRO) and CaCu3Ti4O12/La0.5Sr0.5CoO3/LaAlO3 (CCTO/LSCO) heterostructures in the frequency range 200–4000 cm-1 with a view to study the electronic and phonon properties of the high-dielectric CCTO thin films grown on the SRO and LSCO electrodes by pulsed laser deposition. The frequency dependence of optical conductivity, dielectric, and energy-loss functions of the CCTO films have been calculated by the Kramers-Kronig transformation. Analysis of the optical functions yields two different trends for two compositions, for CCTO/SRO, the electronic behavior is semiconductorlike (carrier concentration N is in the order of 1020 cm-3, optical mass m*/m=0.6, free-carrier relaxation time τ=3·10-14 s) and can be described by applying the Drude-Lorentz model on a plasma of free carriers, whereas for the CCTO/LSCO composition, Lorentz alone oscillator is enough to simulate the electronic part of the conductivity, revealing the presence of bound optically active electrons. We report also on the observation of additional longitudinal phonons at 756, 732, and 708 cm-1 by reflectivity measurements with an oblique beam incidence on CCTO/SRO. The phonons are assigned to Berreman modes. The CCTO/LSCO did not reveal longitudinal phonon modes. Based on the optical spectroscopy results and dc resistivity measurements, we can infer that the CCTO films deposited on a SRO electrode consist of semiconducting grains which are influenced by deposition processing and substrate material. [ABSTRACT FROM AUTHOR] |
