EXAFS study on the local atomic structures around Ce in CeO₂ nanoparticles

CeO₂ nanoparticles coated by sodium bis(2-ethylhexyl) sulfosuccinite have been prepared by using the microemulsion method. An average particle size of 2-3 nm was revealed by using transmission electron microscopy. X-ray diffraction shows that the CeO₂ nanoparticles remain the CaF₂-type cubic structures as the bulk crystal. Extended X-ray absorption fine structure technique is used to probe the local atomic structures around the absorber Ce. A double Gaussian model is used to deduce the structural parameters of the first coordination shell. Bulk CeO₂ with eight oxygen atoms located at 2.338 Å was used as the reference sample to extract the backscattering amplitude and phase shift of the Ce-O bond. Our EXAFS data suggest that in CeO₂ nanoparticles, the oxygen coordination number around Ce has no obvious decrease, but the bond-length of Ce-O is obviously elongated. It is postulated that a surface/core model may be used to describe the local atomic structures in the CeO₂ nanoparticles.