Raman Study of Nanocrystalline-Doped Ceria Oxide Thin Films

Abstract

Samarium-doped ceria (SDC) and gadolinium-doped ceria (GDC) thin films were formed by e-beam vapor deposition on SiO2 substrate, changing the deposition rate and substrate temperature during the deposition. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-Ray spectrometry (EDS) were employed in order to investigate the structure ad morphology of the films. A single Raman peak describing the structure of undoped CeO2 was observed at a frequency of 466 cm−1. Doping of cerium oxide with rare-earth elements shifted the peak to lower frequencies (for Sm—462 cm−1). This shift occurs due to the increased number of oxygen vacancies in doped cerium oxide and it depends on the size and concentration factor of the dopant. It was found that wavenumbers and their intensity differed for the investigated samples, even though the peaks resembled each other in shape. The indicated bands for doped ceria originated as a result of the Raman regime (F2g) of fluorite dioxide associated with the space group (Fm3m). The observed peak‘s position shifting to a lower frequency range demonstrates the symmetric vibrations of oxygen ions around Ce4+ ions in octahedra CeO8. Raman shift to the lower frequencies for the doped samples has two reasons: an increase in oxygen vacancies caused by doping cerium oxide with rare-earth materials and the size factor, i.e., the change in frequency Δω associated with the change in the lattice constant Δa.

Visible Emission on Nanostructured CeO2 Thin Films Obtained by Spray Pyrolysis

“…[17,18] Similar variations in the preferential orientation of ceria thin films with deposition parameters using different deposition methods have been already reported. [20,22,29,32,34] XPS measurements were performed on samples of series 1 to evaluate the chemical composition and the Ce 3þ /Ce 4þ ratio. The general spectra (not shown) confirmed the high chemical purity of CeO 2 films.…”

“…The surface energy of the CeO 2 crystal follows the order (111)>(200)>(220)>(311). [ 22 ] The texturing in the (111) direction means could be related to the fact that the reaction kinetics allows adatom accommodation in the lower energy surface. In series 1, the use of higher flow rates and substrate temperature modifies the accommodation of atoms.…”

“…[ 17,18 ] Similar variations in the preferential orientation of ceria thin films with deposition parameters using different deposition methods have been already reported. [ 20,22,29,32,34 ]…”

“…[6,[13][14][15][16] The use of nanostructured thin films increases the potential applications of this material. [11,17,18] CeO 2 thin films have been prepared by different physical and chemical methods, including flash evaporation, [19] electron-beam evaporation, [20][21][22] sputtering, [3,[23][24][25][26][27][28] laser ablation, [12,[29][30][31][32] and spray pyrolysis. [2,10,11,33,34] In particular, spray pyrolysis is a large-scale production method with advantages such as low cost and versatility when considered as an alternative route to produce thin oxide films.…”

Effect of the Structural and Electronic Properties of Rh/CeXZr1-XO2 Catalysts on the Low-temperature Ethanol Steam-reforming

“…Also, supplementary broadband appears between 540-660 cm -1 were observed for Rh supported catalysts and associated with two different signals, 550 and 600 cm -1 . The first band (~550 cm -1 ) was related to oxygen vacancies generated as charge compensation defects induced by introducing other metal cations into the lattice of CeO2 to maintain the charge neutrality when Ce 4+ ions are replaced by other metal ions [35,36]. The second band (~600 cm -1 ) was assigned to non-stoichiometry oxygen vacancy in the CeO2-like matrix by reducing Ce 4+ to Ce 3+ [35,37].…”