Raman study of Ba-doped ceria nanopowders

A series of Ce1-xBaxO2-y (5 LT = x LT = 0.20) nanometric powders were synthesized by self-propagating 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 F g mode can be well explained with combined confinement and strain effects because of the nanocrystalline powders nature. The appearance of the additional peaks at similar to 560 cm(-1) and similar to 600 cm(-1), are attributed to extrinsic and intrinsic O2- vacancies in ceria lattice. Raman spectra of temperature treated Ce0.80Ba0.20O2-delta sample revealed the instability of this system

Effect of Fe2+ (Fe3+) Doping on Structural Properties of CeO2 Nanocrystals

We have measured the Raman scattering and magnetization of pure and Fe2+(Fe3+) doped CeO2 nanopowders at room temperature. The Raman scattering spectra revealed the existence of CeO2 fluorite cubic structure for all investigated samples. The Raman active mode at about 600 cm(-1), seen in all samples, can be ascribed to the CeO2 intrinsic oxygen vacancies. Additional Raman modes at 720 cm(-1), 1320 cm(-1) and 1600 cm(-1), which appear in the spectra of doped samples, can be assigned to maghemite (gamma-Fe2O3) cation deficient structure, to 2 omega(LO) IR-allowed overtone and two magnon structure, respectively. This implies that our powders are composed of mixed valence states and have defective structure. Presence of oxygen defect states and magnetic ions can be responsible for the observed ferromagnetism at room temperature in both pure and Fe doped samples.Symposium on Raman Scattering in Materials Science, Sep 15-19, 2008, Warsaw, Polan

Hydrothermal Synthesis of CeO2 and Ce0.9Fe0.1O2 Nanocrystals

Pure and 10 mol% Fe3+ doped CeO2 nanocrystals were synthesized by hydrothermal method using two different basic solutions (NH4OH and NaOH). All the samples were calcinated at 140 degrees C and 200 degrees C. The characterization of crystalline structure, vibrational and optical properties was performed using X-ray diffraction, Raman spectroscopy and spectroscopic ellipsometry. The obtained results showed that the Fe-doped samples are solid solutions with different size of nanocrystals, very dependent on the synthesis temperature and type of basic solution. The Raman measurements demonstrated electron molecular vibrational coupling and increase of oxygen vacancy concentration whereas doping provokes a small decrease of optical absorption edge in comparison with pure ceria.International School and Conference on Photonics (PHOTONICA09), Aug 24-28, 2009, Belgrade, Serbi

Spectroscopic ellipsometry and polarimetry for materials and systems analysis at the nanometer scale: state-of-the-art, potential, and perspectives

This paper discusses the fundamentals, applications, potential, limitations, and future perspectives of polarized light reflection techniques for the characterization of materials and related systems and devices at the nanoscale. These techniques include spectroscopic ellipsometry, polarimetry, and reflectance anisotropy. We give an overview of the various ellipsometry strategies for the measurement and analysis of nanometric films, metal nanoparticles and nanowires, semiconductor nanocrystals, and submicron periodic structures. We show that ellipsometry is capable of more than the determination of thickness and optical properties, and it can be exploited to gain information about process control, geometry factors, anisotropy, defects, and quantum confinement effects of nanostructures

One-step preparation and photocatalytic performance of vanadium doped TiO2 coatings

In this paper, we have investigated one-step preparation of vanadium doped TiO2 coatings formed by plasma electrolytic oxidation (PEO) of titanium in electrolyte containing 10 g/L Na3PO4 center dot 12H(2)O + 0.5 g/L NH4VO3. The morphology, phase structure, and elemental composition of the formed coatings were characterized by atomic force microscopy (AFM), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) techniques. Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) was employed to evaluate the band gap energy of obtained coatings. Vanadium doped TiO2 coatings are partly crystallized and mainly composed of anatase phase TiO2, with up to about 2 wt% of vanadium present in the surface layer of the oxide. The valence band photoelectron spectra and UV-Vis DRS showed that vanadium doped TiO2 coatings exhibit notable red shift with respect to the pure TiO2 coatings. The photocatalytic activity was evaluated by monitoring the degradation of methyl orange under simulated sunlight conditions. Photocatalytic activity of vanadium doped TiO2 coatings increases with PEO time. Prolonged PEO times result in higher roughness of obtained coatings, thus increasing surface area available for methyl orange degradation. Vanadium doped TiO2 coatings obtained after 180 s of PEO time exhibit the best photocatalytic activity and about 67% of methyl orange is degraded after 12 h of irradiation under simulated sunlight

Effect of the substrate material on diamond CVD coating properties

Diamond coatings were deposited onto different substrates (Cu, Si, WC-Co, Mo) by hot-filament chemical vapor deposition (CVD). Characterization of the obtained coatings was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, Raman spectroscopy and Fourier transform infrared reflection (FTIR) spectroscopy. The results and observed differences are discussed from the aspect of the chemical nature of the substrate and its reactivity with a gaseous medium. 2003 Elsevier Science B.V. All rights reserved

Crystal structure analysis of Nd-doped ceria solid solutions

This paper deals with Nd-doped ceria solid solutions: Ce(1-x)Nd(x)O(2-delta) with x ranging from 0 to 0.25. Six different powders were synthesized by applying the method based on self-propagating 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)