caa a22 4500 465732461 CHVBK 20180323111745.0 cr unu---uuuuu 170327e19901101xx s 000 0 eng 10.1007/BF02117564 doi (NATIONALLICENCE)springer-10.1007/BF02117564 Defect chemistry of uranium oxides [Elektronische Daten] [K. Naito, T. Tsuji, T. Matsui] Uranium oxides are known as nonstoichiometric compounds whose composition changes according to external conditions such as temperature and oxygen partial pressure. The change of composition caused by the formation of defect structure results in a change of their properties. In this paper, the compositional changes of UO2 and doped UO2 [(U, M)O2; M=La, Ti, Pu, Th, Nb, Cr, etc.] and also those of other uranium oxides (U4O9, U3O8) are shown against oxygen partial pressure. From the results of doped UO2, it is concluded that the valence control rule holds to a first approximation. The defect structures are estimated both from log x vs. log Po2 (x: deviation from the stoichiometric composition and Po2: oxygen partial pressure) and log σ vs. log Po2 (σ: electrical conductivity) relations. The defect structures of UO2 and doped UO2 are derived based on the Willis model for UO2+x. The detect structure of U4O9 phase is similar to that of UO2+x, but the defect structures of U3O8 phase are complicated due to the existence of many higher-order phase transitions. The thermodynamic data such as the partial molar enthalpy and entropy and the heat capacity are important to characterize the defect structure. The high temperature heat capacities of UO2 doped with Gd show pronounced increases at high temperatures the onset temperature decreases as the dopant content increases. The increase of heat capacity is interpreted to be due to the formation of lattice defects. The heat capacity measurements on U4O9 and U3O8 clucidate the presence of the phase transition. The mechanisms of these phase transitions are discussed. Akadémiai Kiadó, 1990 Naito K. Department of Nuclear Engineering, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku, 464-01, Nagoya, (Japan) aut Tsuji T. Department of Nuclear Engineering, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku, 464-01, Nagoya, (Japan) aut Matsui T. Department of Nuclear Engineering, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku, 464-01, Nagoya, (Japan) aut Journal of Radioanalytical and Nuclear Chemistry Articles Springer Netherlands 143/1(1990-11-01), 221-240 0236-5731 143:1<221 1990 143 10967 https://doi.org/10.1007/BF02117564 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF02117564 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Naito K. Department of Nuclear Engineering, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku, 464-01, Nagoya, (Japan) aut NATIONALLICENCE 700 1- Tsuji T. Department of Nuclear Engineering, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku, 464-01, Nagoya, (Japan) aut NATIONALLICENCE 700 1- Matsui T. Department of Nuclear Engineering, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku, 464-01, Nagoya, (Japan) aut NATIONALLICENCE 773 0- Journal of Radioanalytical and Nuclear Chemistry Articles Springer Netherlands 143/1(1990-11-01), 221-240 0236-5731 143:1<221 1990 143 10967 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer