An X-ray Powder Diffraction Study of the Microstructure and Growth Kinetics of Nanoscale Crystallites Obtained from Hydrated Cerium Oxides

Abstract

A detailed analysis of the microstructural properties of nanocrystalline cerium(IV) oxide powders produced by thermal dehydration of two hydrated ceria precipitated from the ceric ammonium and sulfate salts in ammonia solutions is described. In addition, it is shown that the diffraction pattern of hydrated ceria can be modeled with the structure data of CeO 2 and that the average crystallite size for the precursor CeO 2 ‚1.6H 2 O is 19 Å. The analysis of nanocrystalline CeO 2 is based on the modern developments of X-ray powder diffraction line broadening analysis, using 16 Bragg reflections. It is shown that, on average, the crystallites have a spherical shape with volume-weighted and area-weighted diameters in the ranges 264-1349 Å and 178-1079 Å for CeO 2 (am-CeO 2 ) obtained from the ammoniumbased ceria and 263-1756 Å and 195-927 Å for CeO 2 (sul-CeO 2 ) obtained from the sulfatebased ceria. The early stages of the crystallite growth have been studied up to 775 °C and 900 °C, respectively. While sul-CeO 2 is strain-free over the temperature range investigated, am-CeO 2 contains a small amount of strains decreasing with temperature until 700 °C, where strains are negligible. The kinetics of the crystallite growth has been studied for the two samples, from which activation energies have been calculated. Crystallite sizes are also compared to the values from SEM and BET measurements. Strain-free sul-CeO 2 is suggested as a potential candidate as reference material for crystallite size in powder diffraction.

Synthesis of quantum-size cerium oxide nanocrystallites by a novel homogeneous precipitation method

“…The left and right FFTs are from a cubic cerianite particle (marked with CE) and hexagonal La(OH) 3 particle (marked with LA), respectively. The identification of cerianite is consistent with previous opinions that Ce(OH) 4 can be described as CeO 2 ·2H 2 O and dehydrated progressively to CeO 2 ·nH 2 O where n < 2 [18] and that hydrated ceria (CeO 2 ·nH 2 O, n ≤ 2) possesses the same crystalline structure as pure CeO 2 and shows the same XRD patterns [19].…”

Low Temperature Sintering of Gadolinium‐Doped Ceria for Solid Oxide Fuel Cells

“…Second, the weight loss from -150 to 400°C is mainly due to the decomposition of hydroxides on the surface of the powder because the surface of GDC particles is likely covered with a thin hydrated layer given the fact that the GDC powder is made through co-precipitation in water. The proposed weight loss mechanisms are consistent with the previous studies, showing that the desorption of physisorbed H2O from CeC>2 typically occurs at temperatures up to 150°C [36], while complete dehydration takes place between 350 and 470°C, depending on the detailed chemistry of doped CeC>2 [36,37]. By comparing Figs.…”

Nanocrystalline Ce1−xYxO2−x/2 (0≤x≤0.35) Oxides via Carbonate Precipitation: Synthesis and Characterization

“…It clearly shows that the material of a higher yttrium content exhibits a higher activation energy upon coarsening. (24). This phenomena indicates that the crystallite coarsening behavior and mechanism are precursor dependent.…”