Heteroepitaxial thin films of stoichiometric CeO2 and substoichiometric CeOx supported on metal substrates are often used as model systems in studies of the catalytic mechanisms of ceria based catalysts. However, the methods that are being used for the preparation of reduced thin films of ceria produce mostly disordered layers. In a recent paper we have proposed a method of reduction based on the physical vapor deposition of metallic cerium, which is able to produce highly ordered layers of Ce2O3 exhibiting a 4 � 4 LEED pattern reconstruction with respect to CeO2. The observed reconstruction was assigned to the cubic phase of Ce2O3. Here, we have conducted a photoelectron spectroscopy and diffraction study of a transition between CeO2 and Ce2O3 achieved by the proposed method. Results of the photoelectron diffraction study prove the correctness of the assignment of the LEED pattern reconstruction to the cubic phase of Ce2O3. The detailed photoelectron spectroscopy study of the reversible transition in both ways has been interpreted in the light of the high mobility of oxygen atoms in ceria. The reduction of CeO2 layers proceeds from the surface and the oxidation of Ce2O3 layers is realized by oxygen diffusion into the bulk. The transition is observable both at a room temperature and at an elevated sample temperature. Complementary LEED study shows an in-plane lattice constant expansion during the reduction and a contraction during the oxidation, which is interpreted as an effect of a difference between the radius of Ce3+ and Ce4+ ions.

Cubic Ce<sub>2</sub>O<sub>3</sub>? phase studied by photoelectron spectroscopy and photoelectron diffraction

246th National Meeting (2013)

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Cubic Ce2O3? phase studied by photoelectron spectroscopy and photoelectron diffraction

Cubic Ce₂O₃? phase studied by photoelectron spectroscopy and photoelectron diffraction