Electronic structure study of Ce_1−xA_xO₂ (A = Zr & Hf) nanoparticles: NEXAFS and EXAFS investigations

Abstract

Single phase nanoparticles (NPs) of CeO2, Ce0.5Zr0.5O2, Ce0.5Hf0.5O2 and Ce0.5Hf0.25Zr0.25O2 were successfully synthesized by co-precipitation method at constant pH and temperature. The X-ray diffraction results revealed that the additive atoms did not segregate to form secondary phases but led to grain size variation in the NPs. The 10 Dq values in the near edge X-ray absorption fine structure (NEXAFS) spectra at the O K-edge did not vary in the same way as the average grain size was changed for the doped CeO2 NPs. The deconvolution of Ce M5-edge and detailed analysis of O K pre-edge peak have shown the higher Ce(+3)/(Ce(+3) + Ce(+4)) ratio in the Zr- and Hf-doped samples. The local atomic structure around the Ce, Zr and Hf atoms was investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy at Ce K-edge, Zr K-edge and Hf L3-edge, respectively, and the EXAFS data were fitted with the theoretical calculations. The 4f occupancy, Ce(+3)/(Ce(+3) + Ce(+4)) ratio of Ce ions, coordination number of Ce and Ce-Ce/Ce-O bond distances were sensitive to the additive atoms but not explicitly changed according to the grain size variation in the NPs.

X-ray absorption spectroscopy study and photocatalyst application of CuO and Cu0.9Ti0.1O nanoparticles

“…This may be due to the lower ionic radii of Ti than that of Cu and, hence, any substitution of Cu by Ti can lead to decrease in the cell parameters. Similar variations in the metaleoxygen bond have also been observed in the other doped oxide NPs [24,35].…”

“…The shell parameters [coordination number (N), bond-distance (R), and Debye-Waller factor (s 2 )] are presented in Table 1. In the Fourier transformed EXAFS data, the first and second shells arise from the single scattering paths of cation-oxygen and cationecation, respectively [24,32]. Third and other higher shells originate from the single and multi-scattering contributions from a variety of paths and thus larger uncertainties in the third shell fitted parameters have been reported [32].…”

XANES, EXAFS and photocatalytic investigations on copper oxide nanoparticles and nanocomposites

“…For the synthesis of copper oxide photocatalyst materials, we applied previously established coprecipitation method [23][24] with modified strategy. There were three major synthesis schemes used in the present work: (a) In the first scheme, 5 g of Cu(CH3COO) 3 were prepared according to their molar ratio (10 mol% of Ti was taken with respect to Cu) and then mixed together with stirring.…”

Investigation on cation distribution and luminescence in spinel phase γ-Ga3−δO4 : Sm nanostructures using X-ray absorption spectroscopy

“…In this regard, X-ray absorption spectroscopy (XAS), with its two branches of X-ray absorption near edge structure (XANES) and extended X-ray absorption ne structure (EXAFS), becomes the important elemental characterization technique and has been known to be highly sensitive to the local electronic/atomic structure properties and effectively overcomes the issue of sensitivity to the structure and electronic structure characterization of small sized, poorly crystalline or embedded nanostructures. [26][27][28] In the last few years, probing the local symmetry of the diluted doped elements, 29,30 quantication of the valence state changes of host metal ions upon foreign element doping, [31][32][33] changes in the orbital occupancy, 34,35 and variation in the crystal eld effects 36,37 have been studied for various compounds using the XANES. On the other side, EXAFS, due to the sensitivity to the local atomic structure, has become a powerful probing tool for determining the variation in the coordination number and bond lengths of the constituent elements of the probed material.…”