Influence of synthesis time on the morphology and properties of CeO2 nanoparticles: An experimental-theoretical study
2020
Here
we combined experimental and theoretical results to correlate the
morphological, optical, and electronic properties of cerium oxide
(CeO2) prepared by a microwave-assisted hydrothermal method
with varying synthesis times. X-ray diffraction confirmed a cubic
structure without deleterious phases. Density functional theory simulations
confirmed an indirect (K-L) bandgap energy of 2.80 eV, with an electron
transition between O-2p and Ce-4f orbitals, which agrees with the
value obtained using diffuse reflectance. Raman spectroscopy shows
that changing the synthesis times results in samples with different
defect densities at a short range. Theoretical calculations confirmed
that the deformations and changes in the experimental Raman spectra
area result in oxygen displacement; as the displacement decreases,
the crystallinity increases, and only one peak was observed. Scanning
electron microscopy and high-resolution transmission electron microscopy
show changes in the morphologies as the synthesis time varies. For
shorter times, sheet and polyhedral morphologies were noted. With
time increases, the sheets turn into nanorods and nanowires until
the nanowires decrease and cubes are observed. In addition, an initial
study regarding the influence of the surface on the electric response
of CeO2 was completed. It was observed that the presence
of different surface defects ([CeO6·2Vox] or [CeO7·Vox]) can alter the material
resistance.
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