Synthesis and optical properties of La1−XCeXMnO3 studied by infrared reflectivity measurements

The bulk polycrystalline La1−xCexMnO3 (0.0 ≤ x ≤ 0.8) manganites were synthesized through citrate sol-gel auto-combustion method for a wide range of composition 0.0 ≤ x ≤ 0.8. The x-ray diffraction (XRD) analysis suggests the single phase rhombohedral (R-3c) symmetry for parent LaMnO3 compound, however a secondary cubic (Fm-3 m) phase of cerium oxide (CeO2) is appeared when Ce is incorporated into the LaMnO3. A detailed XRD study of these materials were discussed, and specifically the infrared reflectivity measurements on La1−xCexMnO3 materials are discussed in this study for the first time. The phonon softening and hardening was observed for different modes but softening was found to be more pronounced which implied strong electron-phonon coupling. The most affected phonon mode was appeared for the doping range 0.2 ≤ x ≤ 0.4, in which the largest softening was observed. The Lyddane-Sachs-Teller relation is verified by experimental FTIR data.