Near-edge X-ray absorption fine structure spectroscopy and structural properties of Ni-doped CeO2 nanoparticles

Ni-doped CeO₂ nanoparticles were prepared by using the co-precipitation method. The prepared nanoparticles were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The XRD results infer that Ni-doped CeO₂ nanoparticles have single phase nature similar to that of pure CeO₂ nanoparticles. We have calculated lattice parameters using Powder-X software, particle size using Scherer’s formula and strain using the Williamson-Hall method for all the synthesized samples. We have observed a systematic decrease in the lattice parameters, particle size and strain with an increase in Ni doping in CeO₂. The FE-SEM micrographs also confirm that Ni-doped CeO₂ have nanocrystalline behavior and particles are spherical shaped. From the Raman spectra, it is observed that the intensity of classical CeO₂ vibration modes first increases then decreases with Ni doping. The NEXAFS spectra measured at Ce M_4,5 and Ni L_3,2 edges clearly indicate that Ce ions are in the +4 valence state and Ni ions are in the +2 valence state.