Hindawi Publishing Corporation Advances in Materials Science and Engineering Volume 2009, Article ID 502437, 4 pages doi:10.1155/2009/502437 Research Article Structural and Raman Vibrational Studies of CeO 2 -Bi 2 O 3 Oxide System L. Bourja, 1, 2 B. Bakiz, 1, 2 A. Benlhachemi, 1 M. Ezahri, 1 J. C. Valmalette, 2 S. Villain, 2 and J. R. Gavarri 2 1 Laboratoire Mat´ eriaux et Environnement LME, Facult´ e des Sciences, Universit´ e Ibn Zohr, BP 8106, Cit´ e Dakhla, 80000 Agadir, Morocco 2 Institut Mat´ eriaux Micro´ electronique et Nanosciences de Provence, IM2NP, UMR CNRS 6242, Universit´ e du Sud Toulon-Var, BP 20132, 83957 La Garde Cedex, France Correspondence should be addressed to J. R. Gavarri, gavarri.jr@univ-tln.fr Received 10 August 2009; Accepted 1 November 2009 Recommended by Peter Majewski A series of ceramics samples belonging to the CeO 2 -Bi 2 O 3 phase system have been prepared via a coprecipitation route. The crystallized phases were obtained by heating the solid precursors at 600 ◦ C for 6 hours, then quenching the samples. X-ray diffraction analyses show that for x< 0.20 a solid solution Ce 1−x Bi x O 2−x/2 with fluorine structure is formed. For x ranging between 0.25 and 0.7, a tetragonal β ′ phase coexisting with the FCC solid solution is observed. For x ranging between 0.8 and 0.9, a new tetragonal β phase appears. The β ′ phase is postulated to be a superstructure of the β phase. Finally, close to x = 1, the classical monoclinic α Bi 2 O 3 structure is observed. Raman spectroscopy confirms the existence of the phase changes as x varies between 0 and 1. Copyright © 2009 L. Bourja et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. Introduction In the past, several systems based on cerium dioxide CeO 2 (ceria) were extensively investigated for their electrochemi- cal, conduction, or catalytic properties [1–15]. Nanostruc- tured powders of pure and doped ceria can be obtained in various ways [16, 17]. In the present work we deal with the bismuth cerium oxide system CeO 2 -Bi 2 O 3 . This system might be of a high interest for catalytic applications and inte- gration in gas sensors. At present, the cerium bismuth oxide phase diagram (CeO 2 -Bi 2 O 3 ) is not well known. For low Bi fractions, it was clearly established that a solid solution was formed. The substituted phase Ce 4+ 1−x Bi 3+ x O 2−x/2 (V ) x/2 with x < 0.20 (where oxygen vacancies are noted V ) is cubic and its cell parameter increases with x because of size of Bi 3+ ionic radius: r (Bi 3+ ) = 0.117 nm and r (Ce 4+ ) = 0.097 nm [18, 19]. However, above the composition x = 0.20, the nature of phases is not well known. In the present work, we describe a new series of observed phases prepared via a coprecipitation route and after heating at 600 ◦ C. 2. Experimental Fourteenth polycrystalline samples were prepared by mixing bismuth and cerium nitrates solutions (Bi(NO 3 ) 3 , 5H 2 O+ Ce(NO 3 ) 3 , 6H 2 O) and adding NH 4 OH [20, 21] to obtain precipitation of NH 4 NO 3 and bismuth cerium hydroxides. Bismuth compositions ranged from 0% Bi to 100% Bi. The solid obtained by coprecipitation was then heated under air at 600 ◦ C for 6 hours. Experiments carried out at intermediate heating times showed that the observed crystallized phases appear as being stable above heating times of 2 hours. 3. Results The polycrystalline samples were analyzed by X-ray dif- fraction, using a D5000 Siemens-Bruker diffractometer, equipped with a copper X-ray source (wavelength λ = 1.54 10 −10 m; tension V = 45 kV, intensity I = 35 mA), and with a monochromator eliminating K β radiation. The