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

The introduction of lanthanum into the CeO2 structure caused the reduction of almost 5.5% in the surface concentration of Ce(III) species, which are responsible for the 4f-states localized conduction. In this way, the Fermi level shifted towards the valence band (0.20 eV experimentally measured with UV–Vis, and 0.12 eV using ab initio calculations) increasing the total electrical resistance. [Display omitted] •The modification with Lanthanum shifts the so-called band-gap (Eg) in 0.2 eV.•The interaction with CO(g) increase the number of Ce(III) species.•An electron is transferred from Ce3+ to the adsorbed oxygen species onto the surface.•Intrinsic clusters of defects such as [CeO7.Vox]O′ are likely responsible for this behavior.•A decrease in number of electrons at 4f states reduces the hopping electrical conduction. A spectroscopic study of nanostructured lanthanum-doped cerium oxide samples showed that a mild decrease by 5.3% in the surface concentration of Ce(III) species and, a reduction by 0.2 eV in the so-called energy-gap (EF – Ev) after lanthanum addition was sufficient to create the previously reported significant dual behavior when exposed to carbon monoxide at 653 K. The observed X-ray diffraction patterns indicated the presence of a pure fluorite-type crystalline structure. A higher presence of paramagnetic defects clusters, indicated by electron paramagnetic resonance spectroscopy measurements and confirmed by the X-ray photoelectron spectroscopy, was attributed as being responsible for its dual behavior in a CO(g) atmosphere. Theoretical studies have shown the band structure and density of state of the pure and doped material, illustrating the orbitals that participate in the valence band and conduction band. The addition of a small quantity of La3+ converted some Ce3+ into Ce4+, narrowed the “effective band-gap” by 0.2 eV, and created a singly ionized oxygen vacancy species, thus changing the total electrical resistance and creating its dual behavior. The exposure to a reducing atmosphere such as carbon monoxide resulted in a significant increase in defects and converted some Ce4+ into Ce3+ and vice-versa with oxygen atmosphere exposure.