Evolution of the local structure at the phase transition in CeO2-Gd2O3solid solutions

Abstract

We investigated the local environment of the Ce and Gd ions in one of the most important oxygen ion conductors, the CeO 2 -Gd 2 O 3 solid solution, using L III edge extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray absorption near edge spectroscopy (XANES). The average Gd-O distance, as deduced by EXAFS, decreases gradually with increasing Gd content, whereas a sharp decrease in the average Ce-O distance occurs at 25 mol% Gd, accompanying the appearance of structural features characteristic of double fluorite symmetry. An abrupt change in the local environment of Ce, rather than of Gd, is also supported by the XANES spectra. Efforts at stabilizing the oxygen conducting Fm-3m phase in CeO 2 -Gd 2 O 3 solid solutions should therefore concentrate on tailoring the local environment of the Ce ion. We further suggest that our data may provide an explanation for the recently discovered giant electrostriction effect in Ce 0 . 8 Gd 0 . 2 O 1.9 . Since this composition is at the limit of stability of the fluorite phase, local distortions in Ce 0 . 8 Gd 0 . 2 O 1.9 may be modulated by an external electric field more readily than those of the other solid solutions.

Optical investigation of oxygen diffusion in thin films of Gd-doped ceria

“…3a), which is similar to earlier reports [15]. According to XRD, the films are in the fluorite (Fm-3m) phase and have strong (111) texture (Fig.…”

“…There do not appear to be any reports of IS measurements on thin films of GDC20 in the low temperature range that we have used. We note that for T b 200°C, GDC20 exhibits local structural distortions due to the interaction of the cerium host ions (Ce 4+ ) and oxygen vacancies V O [15]. For films, this interaction has been measured to have an activation energy of 1.1 ± 0.2 eV [30].…”

Synthesis and Physicochemical Characterization of Ce1−xGdxO2−δ: A Case Study on the Impact of the Oxygen Storage Capacity on the HCl Oxidation Reaction

“…The experimental EXAFS curves of the CGO nanoparticles closely resemble the curve calculated for the case in which Gd is present on Ce cubic sites as a substitutional solute (black line; see also Ref. for comparison with experimental curves); however, the experimental curves are significantly different from the signature corresponding to pure Gd 2 O 3 . These findings indicate that gadolinium is likely to be successfully incorporated in the host matrix in both cases, and does not form a secondary segregated phase such as Gd 2 O 3 .…”

A review of defect structure and chemistry in ceria and its solid solutions

“…From the positions and relative intensities of peaks 1 and 2 information about local geometry, the number of, and the degree of order in coordinating ligands about the central Ce absorber can be gained. 37,38,116 Similarly, analysis of the relative intensity of peak/shoulder 3 can be used to track the extent of reduction of ceria-based materials. [117][118][119][120] The EXAFS region of the absorption coefficient (which is the focus of the XAFS portion of this review) extends to ca.…”