Synthesis and characterization of Th1−xLnxO2−x/2 mixed-oxides

Several Th1−xLnxO2−x/2 mixed-oxides (Ln = Nd, Sm, Gd, Dy, Er or Yb) were prepared from oxalate precursors. Structural and microstructural investigations of both initial precursors and resulting oxides were undertaken by XRD, μ-Raman spectroscopy and SEM, with a particular attention paid to the Th1−xNdxO2−x/2 series.For oxides, XRD and μ-Raman agreed well with the stabilization of the Fm3¯m structure up to xNd = 0.4, thanks to the concomitant creation of oxygen vacancies, as also confirmed by μ-Raman. Then, a structural transition to the Ia3¯ superstructure occurred. For xNd ≥ 0.49, mixed-oxides with an additional hexagonal Nd2O3 phase were prepared.Besides, the unit cell parameter of the Th1−xLnxO2−x/2 series followed a quadratic relation versus the x substitution rate as a result of the combination between modifications of cationic radius and cation coordination, and the decrease of OO repulsion linked to the presence of oxygen vacancies.

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► Th1−xLnxO2−x/2 (Ln = Nd, Sm, Gd, Dy, Yb) were produced from oxalates precursors.
► The isomorphic thermal conversion of oxalates to oxides were followed by HT-ESEM.
► The stabilization of the ThO2 fluorite structure up to x = 0.4 was evidenced by XRD.
► Neodymium incorporation limits in solid solutions were determined by XRD and μ-Raman.
► Lanthanide incorporation mechanism in ThO2 structure was formally determined by μ-Raman.