K. E. Ivanov

Auger and X-ray photoelectron spectroscopy study of the density of oxygen states in bismuth, aluminium, silicon and uranium oxides

The correlation of relative partial electron density at the oxygen ions with the intensity of Auger O KLL lines in Bi2O3, Al2O3, SiO2 and UO2 has been determined by Auger and X-ray photoelectron spectroscopic methods. The dependence of the relative intensities of Auger O KL2-3L2-3 and O KL1L2-3-lines was characterized from the binding energy of O 1s electrons. The electron density of the outer valence levels of oxygen increases as the relative intensities of Anger OKL2-3L2-3 and O KL1L2-3-lines increase. The fine structure observed in the O KL1L2-3 Auger and the O 2s XPS spectra has been explained by the formation of inner valence molecular orbitals (IVMO) from the interaction of electrons of the O 2s and filled metal ns shells.

XPS Study of Ion Irradiated and Unirradiated UO2 Thin Films

XPS determination of the oxygen coefficient kO = 2 + x and ionic (U(4+), U(5+), and U(6+)) composition of oxides UO2+x formed on the surfaces of differently oriented (hkl) planes of thin UO2 films on LSAT (Al10La3O51Sr14Ta7) and YSZ (yttria-stabilized zirconia) substrates was performed. The U 4f and O 1s core-electron peak intensities as well as the U 5f relative intensity before and after the (129)Xe(23+) and (238)U(31+) irradiations were employed. It was found that the presence of uranium dioxide film in air results in formation of oxide UO2+x on the surface with mean oxygen coefficients kO in the range 2.07-2.11 on LSAT and 2.17-2.23 on YSZ substrates. These oxygen coefficients depend on the substrate and weakly on the crystallographic orientation. On the basis of the spectral parameters it was established that uranium dioxide films AP2,3 on the LSAT substrates have the smallest kO values, and from the XRD and EBSD results it follows that these samples have a regular monocrystalline structure. The XRD and EBSD results indicate that samples AP5-7 on the YSZ substrates have monocrystalline structure; however, they have the highest kO values. The observed difference in the kO values was probably caused by the different nature of the substrates: the YSZ substrates provide 6.4% compressive strain, whereas (001) LSAT substrates result only in 0.03% tensile strain in the UO2 films. (129)Xe(23+) irradiation (92 MeV, 4.8 × 10(15) ions/cm(2)) of uranium dioxide films on the LSAT substrates was shown to destroy both long-range ordering and uranium close environment, which results in an increase of uranium oxidation state and regrouping of oxygen ions in uranium close environment. (238)U(31+) (110 MeV, 5 × 10(10), 5 × 10(11), 5 × 10(12) ions/cm(2)) irradiations of uranium dioxide films on the YSZ substrates were shown to form the lattice damage only with partial destruction of the long-range ordering.

Interaction of neptunyl with goethite (α-FeOOH), maghemite (γ-Fe2O3), and hematite (α-Fe2O3) in water as probed by X-ray photoelectron spectroscopy

The sorption behavior is studied and the physicochemical neptunium species existing on the surface of goethite (α-FeOOH), maghemite (γ-Fe2O3), and hematite (α-Fe2O3) are determined. Solvent extraction and X-ray photoelectron spectroscopy (XPS) are used to determine the neptunium surface species. The ion and elemental composition of the surface of the minerals and surface neptunyl NpO2+ complexes is determined using these data. Compounds containing neptunium(IV) or neptunium(VI) ions do not appear; rather, neptunyl (Np(V)O2+ group is complexed with surface hydroxide groups of α-FeOOH, γ-Fe2O3, and α-Fe2O3. Presumably, the oxygen atoms of iron oxides and water and/or carbonate (CO32-) or nitrate (NO3-) group lie in the equatorial plane of the neptunyl (NpO2+) group.

Inner valence molecular orbitals and structure of the X-ray O4,5(Th,U) emission spectra in thorium and uranium oxides

In the present work, the possibility of an influence of the chemical environment on the structure of O4,5(Th,U) emission spectra of thorium and uranium oxides was studied. It is noted that the fine structure in such spectra is caused by the formation of inner valence molecular orbitals, involving relatively deep Th(U) 6p and O(F) 2s atomic orbitals of the neighbouring atoms. This leads to differences between the O4,5(Th,U) emission spectra of ThO2, ThF4, UO2 and γ-UO3. Also, a comparison between X-ray photoelectron spectroscopy and X-ray emission spectroscopy data was made for the studied compounds. This allowed us to conclude that they are in good agreement.

X-Ray Photoelectron Study of Thorium Silicate ThSiO4 · nH2O and Uranium Silicate USiO4·nH2O

The naturally occurring compounds of thorium ThSiO4, ThSiO4· nH2O, and (Th, Fe)SiO4 and uranium USiO4· nH2O have been studied by X-ray photoelectron spectroscopy in the range of electron binding energies from 0 to 1200 eV. The oxidation state of Th in the natural compounds is close to that in Th(OH)4; for uranium, it is similar to that in UO2. Based on the structure of the low-energy electron spectra it is assumed that the electrons of the filled Th6p- and O2s-atomic orbitals take an active part in chemical bonding. Fine structure was observed in the Th(U)6s-, 5d-, 5p-, 4f-, 4d-, and 4p3/2 electron spectra of all substances under study. Mechanisms of fine structure formation are discussed and the fine structure parameters are correlated with the physicochemical properties of the compounds.

The role of the U6p,5f electrons in chemical bonding of uranyl and uranium fluorides: X-ray photoelectron and X-ray emission studies

Abstract On the basis of the fine X-ray photoelectron (0–∼1000 eV) and X-ray emission (0–∼50 eV) spectral structure parameters as well as results of theoretical calculations of the electronic structure of UO2F2, the study of the U6p,5f electronic states in this compound was done. As a result the U5f atomic orbitals (AO) were established to be able to participate directly in formation of molecular orbitals (MO) in UO2F2. In the MO LCAO approximation it allowed suggestion that in UO2F2 the filled U5f electronic states could exist. This was suggested to be one of the main reasons of significant intensity of valence bands (0–∼15 eV) in X-ray photoelectron spectra (XPS) of the outer valence molecular orbitals (OVMO) and relatively intense peaks (∼96 and ∼103 eV U5d←U5f transitions) in X-ray O4,5(U) emission spectra from UO2F2. Theoretical data also indicated the possibility of participation of the U5f atomic orbitals in formation of the inner valence molecular orbitals (IVMO) (15–∼50 eV binding energy) formed mostly from the U6p and O(F)2s electrons of neighboring uranium and ligands O(F). On the basis of the X-ray O4,5(U) emission spectral structure parameters, the phenomenon of effective formation of such IVMOs first discovered on the basis of the XPS fine structure parameters was confirmed.

XPS study of U, Cs and Sr ionic forms in the “hot” particles formed due to the nuclear power plant accident simulation

The X-iay photoelectron spectroscopy (XPS) ionic and quantitative analysis of the reactor fuel containing masses (FCM) doped with the Cs, Sr ions before and after the up to 2300°C heating, as well as the “hot” particles formed during the laboratory simulated nuclear power plant accident under various conditions, was carried out. The U and Cs were shown to sublime within the first 20 seconds of the heating. Within the next 60 seconds the sublimation of U, Cs and Sr. was shown to take place. The “hot” particles collected within the first 20 seconds of heating and extra heated to 900°C in the air flow were shown to contain 68% of U and 32% of Cs, while the particle collected within the next 360 seconds and extra heated - 51% of U, 13% of Cs, and 36% of Sr. The “hot” particles were suggested to include the uranyl compounds like UO2CO3, Cs2UO4, Cs4UO2(CO3)3, CsUO2(OH)3, SrUO4, Sr3UO6, SrUO2CO3(OH)2. The Ar+treatment of the “hot” particles results in the change of their compositions.

X-ray Spectroscopic Study of U6p,5f Electronic Levels in γ-UO3

The fine structures of X-ray photoelectron (XPE) spectra of low-energy electrons and conversion electron spectra of γ-UO3 (0-40 eV energy) were analyzed taking into account relativistic calculations based on the Xα discrete variation method of the electronic structure of uranium cluster [(UO2)O4]6- (D4h symmetry group) representing the closest coordination of uranium in γ-UO3. The theoretical and experimental data show that U5f electrons directly participate in the chemical bonding. The density of states of 5f valence electrons in uranium trioxide was calculated. At the same time, U6p electrons participate in formation of both inner and outer valence molecular orbitals, and the density of such 6p states in uranium trioxide was also calculated. The order of the inner valence molecular orbitals in the 13-40 eV range was determined, which is of particular importance for development of a procedure to evaluate the uranium-ligand bond distances in axial and equatorial directions in uranyl compounds using their X-ray photoelectron spectra in the range of inner group) representing the closest coordination of uranium in γ-UO3. The theoretical and experimental data showthat U5f electrons directly participate in the chemical bonding. The density of states of 5f valence electronsin uranium trioxide was calculated. At the same time, U6p electrons participate in formation of both inner andouter valence molecular orbitals, and the density of such 6p states in uranium trioxide was also calculated. The order of the inner valence molecular orbitals in the 13-40 eV range was determined, which is of particular importance for development of a procedure to evaluate the uranium-ligand bond distances in axial andequatorial directions in uranyl compounds using their X-ray photoelectron spectra in the range of innermolecular orbitals.

XPS study of the An5f electronic states in actinide (Th, U, Np, Pu, Am, Cm, Bk) compounds.

In the present work it was found that the relative intensity of the quasiatomic An5f- electron line correlates with the number n5f of such electrons in actinide compounds. The experimental dependence of the relative An5f line intensity for Th, U, Np, Pu, Am, Cm, and Bk in various compounds on the number n5f (I5f = 0.02 n5f) in the range from 0 to 7 was obtained. It gave a unique opportunity to determine the oxidation state of actinides in compounds, to conduct the X-ray photoelectron quantitative ionic analysis on the basis of the An5f line intensity, to study the participation degree of electrons in the chemical binding, and to carry out the comparison with the results of the theoretical calculations of the photoemission cross-sections.

X-ray Photoelectron Spectroscopic Study of U- and Cs-Containing Hot Particles Prepared under Laboratory Conditions, Accounting for Parameters of U5f, U4f and Cs3d, Cs4d Electron Lines

X-ray photoelectron spectroscopy was applied to analyzing the elemental and ionic quantitative composition of the pellets of the reactor fuel (UO2) containing 0.3 wt % Cs relative to U, before and after heating the pellets in an argon atmosphere at 2300°C for 1 min, as well as of the resulting hot particles condensed on aluminum supports. Under such fuel heating conditions, cesium ions diffuse to the sample surface and then get partially sublimed. The condensed phase of the hot particles consists predominantly of cesium (62, 48, and 65 at. %) and uranium (38, 52, and 35 at. %) ions for the samples condensed on the foil within the first minute and then additionally heated at 200, 200, and 500°C in air, nitrogen, and nitrogen flows, respectively. Carbonate groups are formed on the surface. Formation of the uranyl compounds Cs2UO4, CsUO2(OH)3, UO2CO3, and Cs4UO2(CO3)3 was presumed.