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Characterization of nanometric multidoped ceria powders
Journal of Alloys and Compounds, 2010
The ceria solid solutions doped with rare earth cations were synthesized by two methods and the microstructural and morphological characterization of powders was performed. The results obtained by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) method and Raman spectroscopy were studied and discussed. The results showed that finer powders have not only higher specific surface area, smaller particles and crystallite sizes, but also larger lattice parameters in the case of both single and multidoped solid solutions.▶ Since the data on the difference in properties between powders in nanomteric range are generally very limited, ceria solid solutions with up to six dopants were prepared and characterized in detail. It turned out that lattice strain was surprisingly higher in coarser powder. On the other hand the results show how the loose nanometric powders with different particle sizes build agglomerate including the pores within. Finer powder forms micropores, while coarser one forms mesopores. Unexpectedly, finer powder flows, which is from technological point of view very important for practical purposes. Powder flow was performed by applying internal comparative method. The same weights of powders were poured into the funnel and the time in which the powder run out of the funnel was measured for each powder. ▶ Since the question of powders history does not have an answer even not to-day, the differences found so far in the literature are usually connected to the particle dimension as measurable parameter. According to the given explanations in our study, we assumed that the different chemical methods and associated thermal effects of MGNP method, opposite to the SPRT-room synthesis, are responsible for differences in the powder properties.
Synthesis and characterization of ceria based nanometric powders
Journal of Power Sources, 2009
Nanopowdered solid solution Ce 1−x Fe x O 2−ı samples (0 ≤ x ≤ 0.1) were synthesized by a self-propagating room temperature synthesis (SPRT). XRD and Raman spectroscopy at room temperature were used to study the vibrational properties of these materials as well as the Fe solubility in ceria lattice. Results show that all obtained powders are solid solutions with a fluorite-type crystal structure and all powders were nanometric in size. The average size of Ce 1−x Fe x O 2−ı particles lies about 5 nm. The results of electrical properties of the sintered samples investigated by an ac impedance spectroscopy are also presented and discussed. It was confirmed that Fe 3+ doped ceria material has a potential as electrolyte for intermediatetemperature solid oxide fuel cell applications.
Ceramics International, 2013
Nanometric ceria powders with fluorite-type structure were obtained by applying self-propagating room temperature method. The obtained powders were subsequently thermally treated (calcined) at different temperatures for different times. Powder properties such as specific surface area, crystallite size, particle size and lattice parameter have been studied. Roentgen diffraction analysis (XRD), BET and Raman scattering measurements were used to characterize the as-obtained (uncalcined) powder as well as powders calcined at different temperatures.
Crystal structure analysis of Nd-doped ceria solid solutions
This paper deals with Nd-doped ceria solid solutions: Ce1-xNdxO2-d with "x" ranging from 0 to 0.25. Six different powders were synthesized by applying the method based on selfpropagating room temperature reaction (SPRT) between metallic nitrates and sodium hydroxide. The method is known to assure very precise stoichiometry of the final product in comparison with a tailored composition. Rietveld refinement was employed to get structural information on the synthesized powder. An increase of Nd ion concentration increases the unit cell parameters and average bond distances. We have shown that all obtained powders were solid solutions with a fluorite-type crystal structure and all powder particles were of nanometric size (about 3 nm).
The influence of synthesis way and dopant on the crystallites size of ceria
Journal de Physique IV (Proceedings), 2005
The present paper deals with the preparation of pure ceria by different methods : a conventional precipitation and a new sol-gel process. The size of crystallites was also carried out, aiming at studying the role of synthesis way on properties of pure ceria. In order to investigate the influence of doping, samples with different molar contents of Mn 2+ were synthesized by co-precipitation. The doping level in all samples is expressed in molar percentage. A linear correlation between the lattice parameters and the Mn content confirm the incorporation of Mn in the ceria lattice. The evolution of crystallites size versus the lattice parameter was investigated.
Journal of Spectroscopy, 2016
The nanopowdery solid solutions of multidoped ceria Ce0.8Nd0.0025Sm0.0025Gd0.005Dy0.095Y0.095O2-δ(x=0.2) with the fluorite type crystal structure of CeO2were synthesized for the first time. Two synthesis procedures were applied: the modified glycine-nitrate procedure (MGNP method) and room temperature self-propagating reaction (SPRT method). All nanopowders were characterized by XRPD analysis, Raman spectroscopy, low temperature nitrogen physisorption, TEM, and SEM methods. According to the XRPD and Raman spectroscopy results, single phase solid solutions of fluorite structure were evidenced regardless of the number of dopants and synthesis procedure. Both XRPD and TEM were analyses evidenced nanometer particle dimensions. The SPRT method results in obtaining sample with higher specific surface area, smaller crystallite and particles sizes, and the same values of the lattice parameter in comparison to pure CeO2. Raman spectroscopy was confirmed to the oxygen vacancies introduced int...
Rare Earth Doped Ceria: The Complex Connection Between Structure and Properties
Frontiers in Chemistry, 2018
The need for high efficiency energy production, conversion, storage and transport is serving as a robust guide for the development of new materials. Materials with physical-chemical properties matching specific functions in devices are produced by suitably tuning the crystallographic-defect-and micro-structure of the involved phases. In this review, we discuss the case of Rare Earth doped Ceria. Due to their high oxygen diffusion coefficient at temperatures higher than ∼500 • C, they are very promising materials for several applications such as electrolytes for Solid Oxide Fuel and Electrolytic Cells (SOFC and SOEC, respectively). Defects are integral part of the conduction process, hence of the final application. As the fluorite structure of ceria is capable of accommodating a high concentration of lattice defects, the characterization and comprehension of such complex and highly defective materials involve expertise spanning from computational chemistry, physical chemistry, catalysis, electrochemistry, microscopy, spectroscopy, and crystallography. Results coming from different experimental and computational techniques will be reviewed, showing that structure determination (at different scale length) plays a pivotal role bridging theoretical calculation and physical properties of these complex materials.
Iranian Journal of Science and Technology Transaction A-science, 2017
Recently, the GDC samples have been synthesized as promising materials for applying in solid oxide fuel cells. In the present research, two different kinds of gadolinium-doped ceria (GDC) nano-composites were prepared by a wetchemical method based on the sol-gel process and new precursors such as CeLH 2 , (pyda.H) 2 [(Ce(pydc) 3 ].2CH 3 OH and (pyda.H) 2 [(Gd(pydc) 3 ].2CH 3 OH, [pydc (2,6-Pyridinedicarboxylic acid), and GdLH 2 , pyda (2,6-diaminopyridine)]. The CeLH 2 and GdLH 2 coordination compounds have been prepared by high-energy ultrasound irradiation. The X-ray powder diffraction (XRD) results showed that the crystal lattice of the compounds (I), (II) was obtained cubic fluorite structures. The scanning electron microscope (SEM) analyses of the compounds (I), (II) indicated that the average grain sizes obtained about 20-30 and 50-70 nm, respectively. The results showed that using high intensity ultrasound can be utilized successfully for the synthesis of supramolecular coordination compounds. Keywords Nanoparticles Á Gadolinium-doped ceria Á Ce(III) complex Á Gd(II) complex Á Solid oxide fuel cell & M. Ranjbar
Cerium oxide based nanometric powders: synthesis and characterization
Science of Sintering, 2007
Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate procedure. Solid solutions of the host compound CeO 2 with one or more dopants in the lattice were synthesized. Rare earth cations (Re = Yb, Gd and Sm) were added to ceria in total concentration of x = 0.2 that was kept constant. The criterion in doping was to keep the value of lattice parameter of ceria unchanged. The lattice parameters were calculated by using the model that takes into account the existence of oxygen vacancies in the structure.