Ce2O3 and CeO2
- Practical Electron Microscopy and Database -
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Cerium forms two well-characterized oxides, tetravalent CeO2 andCe2O3.

Ce2O3 has trigonal symmetry of the space groups P-3m1. The lattice parameters of Ce2O3 are a = 3.89 Å and c = 6.1 Å. In most cases, EELS measurement on Ce2O3 can be unsuccessful because of the rapid oxidation of the sample during its transfer into the TEM system. [1] Figure 4989a shows the measured O-K ELNES without such oxidation. The main structure width, including the three broad peaks A, B and C, was evaluated as the distance between the positions of the broken lines corresponding to the minimum and maximum in the second differentiated spectra.

The measured O-K ELNES

Figure 4989a. The measured O-K ELNES. [2]

Figure 4989b shows the unoccupied partial density of states (PDOS) of Ce2O3 and the bond overlap population diagram (BOPD) between Ce and its neighboring O for the non-core-holed, ground state electronic structures. The main peak structures of the ELNES in Figure 4989a correspond to the Ce5d derived states, which range from 3 to 9 eV above the Fermi level (the Fermi level in Figure 4989b is set to zero). Since the intensities of the BOPD are negative, the corresponding interactions between the Ce and anion O atoms are all antibonding. Larger BOPD intensities correspond to larger spatial overlaps between the two molecular orbitals, promoting higher antibonding energy levels. [3] The spatial overlaps between the Ce5d and the O orbitals show a variation in the Ce5d-derived states, resulting in the energy width of Ce5d PDOS and the main peak structures in the ELNES in Figure 4989a.

The unoccupied PDOS of Ce2O3 and the OPD between Ce and its neighboring F for the non-core-holed, ground state electronic structures

Figure 4989b. The unoccupied PDOS of Ce2O3and the BOPD between Ce and its neighboring O for the non-core-holed, ground state electronic structures. Adapted from [1]

Table 4989. Some surface energies (J/m2) of low-index surfaces of CeO2 crystals.

Solid
(100)
(110)
(111)
CeO2
2.12
1.58
1.09

The cubic phase of ZrO2 is not thermodynamically stable. In practical applications, to stabilize the crystal structures, a small amount of stabilizers  (divalent or trivalent oxides of cubic symmetry) such as MgO, CaO, Y2O3, CeO2, Sc2O3 or Yb2O3 need to be added to stabilize the ZrO2 to the cubic phase.

 

 

 

 

 

 

 

 

 

[1] Ikuo Nishida, Kazuyoshi Tatsumi and Shunsuke Muto, Local Electronic and Atomic Structure of Ce3+-Containing Fluoride/Oxide Determined by TEM-EELS and First-Principles Calculations, Materials Transactions, Vol. 50, No. 5 (2009) 952 - 958.
[2] L. A. J. Garvie and P. R. Buseck: J. Phys. Chem. Solids 60 (1999)1943–1947.
[3] D. G. Pettifor: Bonding and Structures of Molecules and Solids, (Oxford University Press, 1995).

 

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