Structure of Sm- and Gd-doped ceria

In this study some still unexplained structural features of RE-doped ceria (RE≡Sm or Gd) are clarified by the use of synchrotron x-ray powder diffraction. Two structural models are proposed:  a fluoritic one, resembling the CeO2 structure at low RE content, and a hybrid one, intermediate between CeO  and cubic RE2O3, at higher RE content.

C. Artini et al., Inorg. Chem. 54, 4126 (2015)

A structural study of Sm- and Gd-doped ceria was performed with the aim to clarify some unexplained structural features. (Ce1–xREx)O2–x/2 samples (RE ≡ Sm, Gd; x = 0, 0.1, ..., 1) were prepared by coprecipitation of mixed oxalates and subsequent thermal treatment at 1473, 1173, or 1073 K in air; they were then analyzed at room temperature both by synchrotron X-ray diffraction and μ-Raman spectroscopy. Two structural models were adopted to fit the experimental data, namely, a fluoritic one, resembling the CeO2 structure at low RE content, and a hybrid one at higher RE content, intermediate between the CeO2 and the RE2O3 structures. Two main transitions were detected along the compositional range: (a) an RE-dependent transition at the boundary between the fluoritic and the hybrid regions, of a chemical nature; (b) an RE-independent transition within the hybrid region at ∼0.5, having a purely geometrical nature.
The presence of two finely interlaced F- and C-based structures within the hybrid region was confirmed, and hints of their composition were obtained by μ-Raman spectroscopy. The obtained results indicate a possible explanation for the non-Vegard behavioral trend of the cell parameters.

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Structural features of Sm- and Gd-doped ceria studied by synchrotron X-ray diffraction and -raman spectroscopy;
Cristina Artini, Marcella Pani, Maria M. Carnasciali, Maria T. Buscaglia, Jasper R. Plaisier and Giorgio A. Costa,
Inorganic Chemistry 54, 4126 (2015) 
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