Structure and bondings in cerium oxysulfide compounds. I—Electronic, infrared and resonance Raman spectra of Ce2.0O2.5S

✍ Scribed by C. Sourisseau; R. Cavagnat; R. Mauricot; F. Boucher; M. Evain

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 395 KB
• Volume: 28
• Category: Article
• ISSN: 0377-0486
• DOI: 10.1002/(sici)1097-4555(199712)28:12<965::aid-jrs191>3.0.co;2-d

✦ Synopsis

As a Ðrst stage, the electronic (350-900 nm), infrared and Raman (700-10 cm-1) spectra of polycrystalline samples of the oxysulÐde compound were investigated and tentative vibrational assignments are pro-Ce 2.0 O 2.5 S posed from a comparison with the simpler parent compound. Great changes in the vibrational patterns Ce 2 O 2 S demonstrate that the two oxysulÐdes are not isostructural and that the oxidized form cannot be described as a Ce3'-containing peroxide or superoxide system. As a second stage, the resonance Raman spectra of Ce 2.0 O 2.5 S were recorded within the contour of the Ðrst electronic transitions (650-450 nm) on the absorption edge. The Raman excitation proÐles maximize at near 490 nm and exhibit large enhancements for most of the vibrational modes, in particular the higher wavenumber mCe-O equatorial stretching modes at 584 and 548 cm-1. This shows that the resonant electronic transition is more likely an excitonic type and involves a large electronic delocalization, particularly over the cerium-oxygen bonds in the equatorial planes. In conclusion, the compound does Ce 2.0 O 2.5 S not look like as a mixed-valence sample with distinct Ce3' and Ce4' constituent ions, Class II in DayÏs notation, as already known in it is better described as a Ce4'-containing broadband semiconductor in which Ce 4 O 4 S 3 ; low-energy excitonic-type transitions implying the intermediate 4f levels have to be considered and in which valences do not appear to be Ðrmly trapped.