Abstract
Cerium oxide nanoparticles (∼3–20 nm in diameter) made by a vapor phase condensation method, have been studied by several methods of transmission electron microscopy (TEM): electron energy loss spectroscopy (EELS), high resolution imaging, and electron diffraction. The white-line ratios of the EELS spectra were used to determine the relative amounts of cerium ions and as a function of particle size. The fraction of ions in the particles rapidly increased with decreasing particle size below ∼15 nm in diameter. The particles were completely reduced to at the diameter of <∼3 nm. This reduced cerium oxide has a fluorite structure which is the same as that of bulk Also, EELS spectra taken from the edge and center of the particle indicated that for larger particles the valence reduction of cerium ions occurs mainly at the surface, forming a layer and leaving the core as essentially A micromechanical model based on linear elasticity was used to explain the lattice expansion of the nanoparticles. Comparing our results with previously published works indicates that the amount of in nanoparticles is a strong function of the particular synthesis methods used to make these particles.
- Received 7 November 2003
DOI:https://doi.org/10.1103/PhysRevB.69.125415
©2004 American Physical Society