{sup 151}Eu-Moessbauer spectroscopic and X-ray diffraction study on Eu {sub y}M{sub 1-y}O{sub 2-x} (0 {<=} y {<=} 1.0) (M = Th, U)
- Department of Materials Science, Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan)
- Department of Chemistry, Hokkaido University, Sapporo 060-0810 (Japan)
{sup 151}Eu-Moessbauer spectroscopic and powder X-ray diffraction (XRD) study has been performed for the Eu {sub y}M{sub 1-y}O{sub 2-x} (M = Th and U) systems over the entire composition range of 0 {<=} y {<=} 1.0. The XRD results of the Eu-Th system showed that a very wide defect-fluorite (DF) type phase in which oxygen vacancies (V {sub O}) are disordered (x = y/2) is formed for 0 {<=} y < 0.5 and that two-phase regions sandwitching a narrow C-type (C) single phase around y {approx} 0.8 appear for 0.5 < y < 0.8 (DF + C) and 0.82 < y < 1.0 (C + B-type (monoclinic) Eu{sub 2}O{sub 3}). The Moessbauer results show that the isomer shifts (ISs) of Eu{sup 3+} in this system smoothly increase with Eu composition, y. The decrease of average coordination number (CN) of O{sup 2-} around Eu{sup 3+} with increasing y (CN = 8 - 2y) (x = y/2) results in the decrease of the average Eu-O bond length, which is due to the decrease of repulsion force between O{sup 2-} anions. This result confirms that the IS of Eu{sup 3+} correlates well with the average Eu-O bond length in oxide systems. For the Eu-U system, the lattice parameter, a {sub 0}, of the system decreases almost linearly with y, in accordance with the calculated a {sub 0} versus y curve for the oxygen-stoichiometric (i.e. x = 0) fluorite-type dioxide (CN = 8). The ISs of Eu{sup 3+} in this composition range remain almost constant around 0.5 mm/s, which is comparable to those of pyrochlore oxides (Eu{sub 2}Zr{sub 2}O{sub 7} and Eu{sub 2}Hf{sub 2}O{sub 7} (y = 0.5)) with O{sup 2-}-eight-fold coordinated Eu{sup 3+}(CN = 8)
- OSTI ID:
- 20889759
- Journal Information:
- Materials Research Bulletin, Vol. 40, Issue 4; Other Information: DOI: 10.1016/j.materresbull.2005.01.003; PII: S0025-5408(05)00022-X; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0025-5408
- Country of Publication:
- United States
- Language:
- English
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