Reactive Ce0.8RE0.2O1.9 (RE = La, Nd, Sm, Gd, Dy, Y, Ho, Er, and Yb) Powders via Carbonate Coprecipitation. 1. Synthesis and Characterization

Nanocrystalline powders of ceria doped with 20 at. % of various rare-earth cations (Ce 0.8 RE 0.2 O 1.9, RE = La, Nd, Sm, Gd, Dy, Y, Ho, Er, and Yb) have been synthesized via coprecipitation using ammonium carbonate as the precipitant. The precursors and the resultant oxide powders were characterized by chemical analysis, differential thermal analysis/thermogravimetry (DTA/TG), X-ray diffractometry (XRD), and high-resolution scanning electron microscopy (HRSEM). The radius of RE 3+ cations was found to have appreciable effects on chemical composition, thermal behavior, and particle morphology of the precursors and crystallite growth of the resultant oxide powders. The precursors obtained in this work possess a general formula of (NH 4 ) x CeRE 0.25 (CO 3 ) 1.875+ x /2 · y H 2 O ( x = 1 and y = 1 for RE = La, Nd, and Sm; while x = 0.25 and y = 2 for the rest), which decompose into oxides via oxycarbonate intermediates up to ≈410 °C upon heating. The precursors doped with RE 3+ cations smaller than Sm 3+ mainly consist of discrete primary particles of spherical shape, while those with larger cations (La 3+, Nd 3+, and Sm 3+ ) are mainly composed of secondary agglomerates of fibrous primary particles. The fluorite-structured Ce 0.8 RE 0.2 O 1.9 solid solutions are formed during calcination without any second phase detected with XRD, and the lattice parameters increase almost linearly with increasing ionic radius of the dopant. The coarsening rate of Ce 0.8 RE 0.2 O 1.9 crystallites during calcination varies with the radius of RE 3+ cations, being highest for Ce 0.8 Sm 0.2 O 1.9 while lowest for Ce 0.8 La 0.2 O 1.9 .