Experimental and theoretical interpretation of the order / disorder clusters in CeO2:La

The data shows the formation of polycrystalline cerium oxide systems with a reduction in the number of paramagnetic species after lanthanum doping. The UV-Vis measurements depict a reduction of 0.20eV in the effective energy-gap after the introduction of trivalent [La(III)] rare-earth species, while theoretical calculations showed a reduction of 0.12eV. The most contribution to the electrical response comes from Ce-f localized states near the Fermi level and their interaction with defective clusters of oxygen and metallic species.
The energy difference between the conduction band and the Fermi level (Ec - Ef) increases because of the modification with La(III), with a consequent decrease in the number of available electrons for conduction besides an increase of the initial electrical resistance of the L.D.C sample. After exposure to a reducing atmosphere (CO gas) at 673K, it provided energy to a great number of electrons that were easily available for conduction, thereby decreasing the sample electrical resistance. This was direct proof of an increase of the oxygen vacancies along with the consequent reduction of the Ce(IV) → Ce(III) reaction.