Avenue Albert Einstein, 69626 Vi/leurbanne, France A copper-cerium oxide sample prepared with an atomic ratio, Cu : Ce, of 0.01 has been studied by electron paramagnetic resonance (EPR) spectroscopy. A well resolved spectrum of copper(11) ion pairs has been evi denced and the hyperfine structure of the perpendicular components clearly appears. The high resolution can be explained by the presence of two nearly equivalent Cu2+ ions separated by an oxygen ion. A correlation in EPR parameters has been found between the signal corresponding to a single Cu2+ ion, a precursor of the dimer, and the copper(11) ion pair spectrum.

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Ceria reduction under hydrogen leads to a fluorite lattice expansion between 573 and 1073 K. Both bulk reduction of Ce4' ions and insertion of hydrogen are thought to be responsible for this expansion in the 573-843 K temperature range.

Conditions for preparing copper-cerium mixed oxides by coprecipitation have been examined. X-Ray diffraction (XRD), electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the oxides calcined at different temperatures up to 1073 IS. In all cases, a solid solution is formed by the insertion of Cu2+ ions in substitutional Paper 5/04920B;