Self-propagating Room Temperature Research Articles

Room-temperature synthesis of nanometric α-Bi 2O 3

Nanometric Bi 2O 3 powder was successfully synthesized by applying the method based on self-propagating room temperature reaction (SPRT) between bismuth nitrates and sodium hydroxide. X-ray powder diffraction (XRPD) and Rietveld's structure refinement method were applied to characterize prepared powder. It revealed that synthesized material is a single phase monoclinic α-Bi 2O 3 (space group P2 1/ c with cell parameters a = 5.84605(4)Å, b = 8.16339(6) Å, c = 7.50788(6) Å and β = 112.9883(8)). Powder particles were of nanometric size (about 50 nm). Raman spectral studies conformed that the obtained powder is single phase α-Bi 2O 3. Specific surface area of obtained powder was measured by Brunauer–Emmet–Teller (BET) method.

Synthesis and characterization of the nanometric Pr-doped ceria

In this paper nanometric powders of solid solution of the host compound ceria (CeO 2) with Pr dopant in the lattice were synthesized by self-propagating room temperature (SPRT) synthesis with composition (Ce 0.9Pr 0.1O 2− δ ). Powder properties such as specific surface area crystallite and particle size and lattice parameters have been studied. BET, TEM, X-ray diffraction (XRD) analysis and Raman scattering measurements were used to characterize the samples at room temperature. Obtained solid solution exhibits a fluorite-type crystal structure. The average crystallite size is about 3–4 nm. Williamson–Hall plots were used to separate the effect of the size and strain in the nanocrystals. It is noticed the redshift and asymmetric broadening of the Raman F 2g mode which is explained with nanocrystalline nature of powders. Color characters of solid solution depending on calcinations temperature and their position in the chromaticity diagram were studied by UV–vis spectrophotometry (diffuse reflectance).

Synthesis and characterization of ceria based nanometric powders

Nanopowdered solid solution Ce1−xFexO2−δ 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 Ce1−xFexO2−δ 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 Fe3+ doped ceria material has a potential as electrolyte for intermediate-temperature solid oxide fuel cell applications.

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).

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).

Raman scattering from low frequency phonons confined in CeO2 nanoparticles

CeO2 nanopowder samples synthesized by self-propagating room temperature method were investigated by Raman spectroscopy. The phonon modes observed in the low frequency region (ω < 70 cm-1) can be well described by the elastic continuum model, assuming that nanoparticles are of perfect spherical shape and isotropic. Both rigid boundary and stress-free surface cases were analyzed. The calculated vibrational frequency dependencies on the particle diameter were used to identify the modes: (l =2, n = 0), (l = 0, n = 0) and (l = 0, n = 1). Using the facts that mode frequencies scale inversely with particle dimension (ω ∼ 1/D) and that mode-radiation coupling coefficient for this type of vibrations is 1/ω, the correspondence between the particle size distribution and the Raman intensity was made. Particle diameter values ranging from 7 to 8 nm for the rigid boundary condition give the best description of the experimental spectra. This coincides well with the average particle diameter value of 8 nm acquired from the phonon confinement model.

Raman study of Ba-doped ceria nanopowders

A series of Ce1-xBaxO2-y (5?x?0.20) nanometric powders were synthesized by selfpropagating room temperature synthesis. XRD and Raman scattering measurements were used to characterize the samples at room temperature. All the samples are solid solutions with fluorite type structure with an average crystallite size about 5 nm. The redshift and asymmetric broadening of the Raman F2g mode can be well explained with combined confinement and strain effects because of the nanocrystalline powders nature. The appearance of the additional peaks at ~ 560 cm-1 and ~ 600 cm-1, are attributed to extrinsic and intrinsic O2- vacancies in ceria lattice. Raman spectra of temperature treated Ce0.80Ba0.20O2-d sample revealed the instability of this system.

Ce1−xY (Nd)xO2−δ nanopowders: potential materials for intermediate temperature solid oxide fuelcells

Nanopowdered solid solution Ce1−xY (Nd)xO2−δ samples (0.1≤x≤0.25) were made by self-propagating room temperature (SPRT) synthesis. The first-order Raman spectraof Ce1−xY (Nd)xO2−δ samples measured at room temperature exhibit three broad features: the main Raman activeF2g mode atabout 450 cm−1 and two broad features at about 550 (545) and600 cm−1. Themode at ∼600 cm−1 was assigned to the intrinsic oxygen vacancies due to thenonstoichiometry of ceria nanopowders. The mode at about 550 (545)cm−1 was attributed to the oxygen vacancies introduced into the ceria lattice wheneverCe4+ ions are replacedwith trivalent cations (Y3+, Nd3+). The intensity of this mode increases with doping in both series of samples, indicating a change ofO2− vacancy concentration. The mode frequency shifts in opposite direction in Y- and Nd-dopedsamples with doping level, suggesting that different types of defect space can occur inY- and Nd-doped ceria nanopowders.

Reaction of Ce&lt;sub&gt;1-x&lt;/sub&gt;Re&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;2-δ&lt;/sub&gt; Nanopowders Synthesis

One of the methods for powder synthesis that is both cost and time effective is the selfpropagating room temperature synthesis. We applied this method to synthesize rare earth doped ceria nanopowders. Since they exhibit very high ionic conductivity at intermediate temperatures these compositions are attractive for a new generation of nanostructured ceramics applicable in solid oxide fuel cells as electrolytes. In this paper we paid our attention to the reaction based on methathetical pathway, whereby solid solution nanopowders of rare earth elements with ceria were obtained at room temperature. Compositions of Ce1-xRexO2-δ (Re = Y , Nd) were synthesized with x ranging from 0 to 0.20. The reaction course is discussed and the properties of the obtained powders are presented.

The size and strain effects on the Raman spectra of Ce 1− xNd xO 2− δ (0≤ x≤0.25) nanopowders

Ultrafine Ce 1− x Nd x O 2− δ ( x=0–0.25) powders were synthesized by self-propagating room temperature synthesis. Raman spectra were measured at room temperature in the 300–700 cm −1 spectral range. The shift and asymmetric broadening of the Raman F 2g mode at about 454 cm −1 in pure and doped ceria samples could be explained with combined size and inhomogenous strain effects. Increased concentration of O 2− vacancies with doping is followed by an appearance of new Raman feature at about 545 cm −1.

Self-propagating room temperature synthesis of nanopowders for solid oxide fuel cells (SOFC)

Ceria based solid solutions are promising ceramic electrolytes for SOFC which will be able to function at intermediate temperatures. In accordance with common trends to decrease the production and operating costs of new generation of SOFC materials the reaction based on metathetical pathway is described, whereby solid solution powders of rare earth doped ceria in the nanoscale range were obtained at room temperature. By simple hand mixing of reactants the reaction was enhanced, propagating afterwards by itself. Nanometric ceria powders doped with Y or Nd, as well as co doped with both cations were synthesized. Composition of Ce 1 − x Me x O 2 − y ranged from x = 0–0.25. The reaction course is described in detail and the properties of the obtained powders are presented.