Anharmonicity around Th in crystalline oxide-type compounds: An in situ-, high-temperature XAFS spectroscopy study to 1500 degrees C

Abstract : The local atomic structures around Th in polycrystalline thorianite (ThO(2)) and thorite (alpha-ThSiO(4)) have been measured using Th L(III)-edge XAFS spectroscopy from room temperature to 1500 degrees C. Up to 48 spectra have been collected using the energy-dispersive mode and the heat-loop technique. Asymmetry in the Th-O pair distribution function at all temperatures has been accounted for using several anharmonic models. When the best model is used (the analytic model from Crozier and coworkers), the XAFS-derived thermal expansion, alpha, of the Th-O bond (i.e., 10(2) and 8(2) x 10(-6) K(-1) in crystalline ThO(2) and alpha-ThSiO(4), respectively) an consistent with theoretical predictions (8 x 10(-6) K(-1), Hazen and Finger's law) and the previous results (9.98 x 10(-6) K(-1) at 1500 degrees C or 9.67 x 10(-6) K(-1) at the temperature ranges of 20-2000 degrees C) obtained by using X-ray and neutron diffraction techniques. In thorite, where two sets of individual Th-O distances occur (at 2.37 and 2.47 Angstrom), the longer bonds are found to expand the most as compared to the shorter ones, again in good agreement with theoretical predictions. Based on this model, the medium-range local structure is found to exert little influence on the Th-O bond thermal expansion with increasing temperature. Therefore, anharmonicity for the Th-O bond is found to depend basically on the coordination geometry around thorium. Then, the same anharmonic model can be used to model the evolution of the local structure around Th as a function of temperature in related-, but structurally more complex materials such as radiation damaged ceramics, glasses and melts for nuclear wastes. (C) 1999 Elsevier Science B.V. All rights reserved.
Document type :
Journal articles
Complete list of metadatas

https://hal-upec-upem.archives-ouvertes.fr/hal-00693888
Contributor : Admin Lge <>
Submitted on : Thursday, May 3, 2012 - 9:02:46 AM
Last modification on : Thursday, May 3, 2012 - 9:02:46 AM

Links full text

Identifiers

Collections

Citation

Zh Wu, F Farges. Anharmonicity around Th in crystalline oxide-type compounds: An in situ-, high-temperature XAFS spectroscopy study to 1500 degrees C. Physica B: Condensed Matter, Elsevier, 1999, 266 (4), pp.282--289. ⟨10.1016/S0921-4526(99)00057-5⟩. ⟨hal-00693888⟩

Share

Metrics

Record views

76