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Recent measurements of the uranium dioxide heat capacity are analysed in the temperature range RT-8000 K. The high temperature behaviour of C(p)(T) is essentially governed by heat energy exchange mechanisms in the solid, involving formation of atomic and electronic defects. The analysis is centred on the interpretation of the lambda-transition observed in the region of 0.8T(m), interpreted on the basis of cooperative formation of anion Frenkel defects. Electronic defects, in the form of localised small polarons, formed in the same temperature range, are demonstrated to provide a minor contribution to C(p), due to electron-hole interaction. Schottky defects are predicted to play an effective role only between 2700 K and T(m). The decrease of the heat capacity above the melting point is explained as a saturation of the thermally activated defect formation. The heat capacity in the liquid is sustained by molecular vibrations up to 4500 K; only at higher temperatures do more energetic, electronic excitations take place. The formation of defects in the solid is described using mean-field models which are able to reproduce the observed transition and its dependence on stoichiometry in UO(2 +/- x).

Additional information

Authors: RONCHI C, JRC Karlsruhe (DE);HYLAND G J, University of Warwick, Department of Physics, Coventry (GB)
Bibliographic Reference: Paper presented: International Conference Actinides '93, Santa Fe (US), September 19-24, 1993
Availability: Available from (1) as Paper EN 37887 ORA
Record Number: 199311360 / Last updated on: 1994-11-28
Original language: en
Available languages: en