PROBING STRUCTURAL PROPERTIES AND DEFECTS OF DOPED CERIa-based materials BY IN SITU HIGH TEMPERATURE rAMAN SPECTROSCOPY
WG3 members: Soghomon Boghosian, Antonios Tribalis
homepage: www.iceht.forth.gr/staff/boghosian.html
One of the home-made in situ Raman optical reactor cells during operation. Laser line: Ar+ 514.5 nm
Structural defects occurring in the ceria cubic matrix upon doping or mixing with other metal oxides (e.g. ZrO2, La2O3 etc) are probed with in situ Raman spectroscopy. Monitoring the spectral features under oxidative/reductive atmospheres provides information on the oxide material reducibility. Ceria, with a fluorite-type cubic structure, space group Fm3m (Oh5), has an exceptionally simple vibrational structure with one Raman active mode (F2g), typically observed at 465 cm-1 and is due to symmetric breathing mode of O atoms surrounding each Ce4+. Because this vibrational mode is only dependent of the Ο movement, its band characteristics (width and position) are extremely dependent on the disorder induced in the oxygen ion sublattice of the oxide and is therefore sensitive to both Ce–O bond arrangements and lattice defects. Punctual defects may exist even in pure ceria, caused by the non-stoichiometric condition due to the presence of Ce3+. The resulting effective negative charge is compensated by O vacancies in the pure ceria sublattice.
