[en] Selective sorption has been examined under static and dynamic conditions for various modifications of SKK and SFKK antimony-bearing sorbents by the use of the highly charged ions UO²⁺₂, Ce³⁺, Pu³⁺, Pu⁴⁺, Th⁴⁺; modification of the initial phase composition and structure enables one to adjust the selectivity for the actinides

[en] Physicochemical properties of VO₂(NO₃)₂x2Bu₃PO and U(NO₃)₄x2Bu₃PO complexes have been investigated. Values of the complex solubility in water, pure diluents and also in the presence of a salting-out and of the excess of the organic complexing agent have been determined. The effect of the temperature and aqueous and organic phase content on the complex distribution in the two-phase decane-water system has been found out

[en] The complexes of uranium (6) and (4) nitrates with trialkyl-phosphine oxides (TAPO) have been synthetized, and qeneral methods of their synthesis, separation and purification described. It has been found that, whatever the method of preparation, each compound of the synthesized homologous series of complexes corresponds only to disolvate stoichiometry of a qeneral formula, UO₂(NO₃)₂ x 2(Csub(n)Hsub(2n+1))₃PO and U(NO₃)₄ x 2(Csub(n)Hsub(2n+1))₃PO. It is shown that the complexes prepared do not contain water and nitric acid. The absence of water and acid in the complex composition, as well as the possibility of preparing the same compounds by the methods where no nitric acid is used, make it possible to believe that formation of acidocomplexes is unlikely. The described methods pf complex synthesis may be of use for preparative and analytical purposes in separating (quantitatively, in some cases) complexes of actinide, rare-earth, noble, transplutonium, and other elements with phosphates, phosphinates, phosphine oxides, di- and polyoxides, as well as with other organic ligands. The experimental data on the thermal properties of the complexes separated are presented

[en] Using the methods of vibrational spectroscopy and thermal analysis the series of uranyl oxalate complexes with trialkylphosphates of the generic formula UO₂C₂O₄xR₃PO₄, where R=CH₃-C₄H₉, has been stUdied. IR absorption spectra of the compounds are obtained in the 4000-300 cm^-1 frequency range. It is found that in the series of compounds investigated neither the length of hydrocarbon radical, nor any variant of its spatial location produce any considerable effect on the vibrational frequency values of the main functional groups. Spectral properties of the complexes are compared with a similar UO₂C₂O₄xR₃PO series. It is established that in the complexes with tertiary aliphatic phosphineoxides the UO₂²⁺ ion vibration frequencies are approximately 20 cm^-1 lower than those of the corresponding phosphates. The method of thermal analysis is shown to be more sensitive to variations in the UO₂²⁺ bond strength with the phosphorus-containing organic ligand. Temperature ranges for removal of aliphatic phosphates and phosphineoxides differ almost by 100 deg C. The thermal decomposition of the compounds studied is investigated

[en] Mass transfer and cation diffusion mechanisms on the surface of UO_2 nanocrystal were investigated by the high-speed MD method using GPU. Stoichiometric uranium dioxide nanocrystals of 12,000 ions were simulated with two interaction potentials sets. Three regions on the nanocrystal surface with significantly different activation energies were separated. It is shown that the overall mass transfer on the surface is limited by the diffusion of cations on edges connecting (1 0 0) facets. The calculated diffusion activation energy of 5.2 eV is close to the experimental one of 4.7 eV. Estimations of the thickness of the diffusion surface layer were carried out. It is shown that the diffusion of cations in the bulk is fully associated with the migration of Schottky cation vacancies, which are formed on (1 0 0) surfaces. The calculated formation energy of a Schottky trio of 6.6 eV is close to the experimental estimation of 6.5 eV, but significantly differs from the value of 9.8 eV, derived by the standard lattice statics method

[en] By high-speed MD method using GPU the CGO nanocrystals of about 40,000 particles during about 0.1 μs, in the temperature range (2500–700) K, were simulated. The influence of different dopant distributions on the nanocrystal characteristics, for two potentials sets, was investigated. For a given potentials set Gd distribution does not affect the lattice parameter and the anion diffusion coefficients. Five types of impurity vacancies were defined, by the Gd number in the nearest neighborhood, and temperature dependences were built. The formation energies of vacancies of all types were obtained. Calculated by the MD conductivity activation energy of 0.6 eV acceptable coincides with the experimental 0.7 eV, just as the absolute conductivity values. The supposition that helium in CGO ceramics dissolve in vacancies, surrounded only by cerium ions, was discussed. Analysis of the MD, conductivity measurements and helium defectoscopy shows that up to the melting temperature the vacancies are mainly associated with impurity ions

[en] Using the methods of vibrational spectroscopy and thermal analysis a number of uranyl complexes with trialkylphosphine oxides of the general formula UO₂(NO₃)₂x2R₃PO, where R-C₂H₅-C₁₀H₂₁ have been studied. Infrared and Raman spectra are interpreted according to vibration types. Comparison of vibrational spectra of the complexes in solid phase and solutions of organic solvents permitted to find the differences in position and amount of acids responsible for complexing. It is detected that in the series of complexes investigated the strength of uranyl bond with phosphoryl group oxygen practically remains stable, whereas degree of covalence of nitrate groups is observed. The pointed out peculiarities are interpreted proceeding from the presence of bridge nitrate groups in the structure of the complexes. Thermal stability of the complexes is studied, chemism of their decomposition being suggested

[en] Highlights: • We derived the degree of vacancy association in Schottky defects from temperature. • At high temperatures cation vacancy forms complexes with anion vacancies. • Point defects model in the presence of complexes was considered. • The presence of anion vacancies around cation vacancy lowers its migration energy. • The formation of nanovoids at high cation vacancy concentrations was shown. - Abstract: Mass transfer processes in fluorite-type systems are determined by the diffusion of cations via vacancies from Schottky defects. To predict diffusion coefficients of cations and other parameters based on it the Lidiard and Matzke approximation of the point defects model, namely the assumption of isolated vacancies, is widely used. States of the Schottky defect were studied with the high-speed molecular dynamics method in a wide temperature range, with six different interaction potentials. Schottky vacancies were dynamically detected during the simulation. It is shown that contrary to the Lidiard and Matzke model, the Schottky cation vacancy is always associated with anion vacancies. The degree of the Schottky defect association depends on the temperature, at high temperatures near the cation vacancy two or more anion vacancies are located. It is shown that the calculated formation energy of Schottky defects in the form of the trivacancy (5.8–7.4) eV for all potentials are close to the experimental value (6–7) eV, in contrast to the formation energy of Schottky defects in the form of isolated vacancies that exceeds 10 eV. Point defects model of the simulated system in the presence of an artificially created Schottky defect was constructed and compared with calculation results. According to our study the point defects model is applicable only at low temperatures less than half of the melting temperature. It is shown that the presence of anion vacancies near the cation vacancy reduces the migration energy of cations. However, for systems with several Schottky defects the vacancy clusterization and the formation of voids are observed. This leads to an increase of the diffusion activation energy due to the contribution of the energy that needs to separate the single cation vacancy from the void

No abstract available

[en] Highlights: • Stepped shape of anion MSD curve is caused by the formation of intrinsic defects. • At least one defect should exist in system to properly study intrinsic diffusion. • We resolved the contradiction between lattice statics and molecular dynamics results. • Mechanism of exchange diffusion of anions has been studied in detail. - Abstract: Literature analysis reveals a significant discrepancy in the anion diffusion activation energies, calculated by the MD and the lattice statics methods using the point defects model, for a given interaction potentials set. To clarify this issue, the anion diffusion mechanisms and defect concentrations in a wide temperature range have been studied in detail. The stepped shape of the mean squared displacement (MSD) curves of anions, observed at low temperatures, is caused by the spontaneous formation and subsequent recombination of the long-living anion Frenkel defect. It is shown that correct MSD can be obtained, if at least one thermally activated defect exists (on average) in the simulation box. Otherwise the anion diffusion coefficients depend on the supercell size. Using the concentrations of defects and their mobility, calculated by the MD method, the diffusion coefficients of anions in the low-temperature region were calculated. They coincide well with the experimental data in absolute values. The mechanism of exchange diffusion has been quantitatively studied for the first time. Methods for detecting single exchange acts and calculating MSD for each type of exchange chains were developed. It is shown that exchange diffusion gives the greatest contribution at medium temperatures, before the superionic transition.