Structural and spectroscopic characterization of CeO2-TiO2 mixed oxides

Mixed CeO2-TiO2 systems have been synthesized using the sol-gel technique in a symmetric range of nominal compositions (10{,} 50 and 90 mol% CeO2). The solid materials were characterised using a variety of diffractometric and spectroscopic techniques. The intimate contact between the two components during the synthesis leads to heterogeneous systems which are based on the presence{,} besides the two individual oxide phases{,} of a mixed phase of a cerium titanate (Ce2Ti2O7{,} pyrochlore structure) which contains Ce3+ ions that impart particular optical properties to the solid (a pronounced red shift with respect to the band gap transition of the two oxides). Ce3+ ions are present at the surface of the systems together with tetravalent Ce and Ti ions. The mixed solids can be reduced by annealing under vacuum and{,} upon reoxidation under mild conditions with O2{,} form superoxide species adsorbed on Ce4+ which have{,} as already reported for low loading CeO2-TiO2 systems{,} peculiar spectroscopic properties with respect to superoxide adsorbed on bare cerium dioxide.