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Teterin, Yu. A.; Ryzhkov, M. V.; Teterin, A. Yu.; Панов, А. Д.; Nikitin, A. S.; Иванов, К. Е.; Utkin, I. O.

doi:10.1023/a:1020390220075

Cited by 16 publications

(67 citation statements)

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“…cluster with O h symmetry and the experimental differences in the binding energies of the outer and inner electrons of uranium [27], as well as of UO 3 (see, e.g., [5,28]), allow construction of the molecular orbital scheme in the MO LCAO approximation (Fig. 2).…”

Section: Resultsmentioning

confidence: 99%

“…Correct analysis of the fine structure of the X-ray photoelectron, conversion, and O 4,5 (U)-emission spectra of UO 2 and UO 3 was precluded by the lack of the results of relativistic calculations of their electronic structure. For UO 3 , such calculations were recently carried out, which allowed full identification of the fine structure of the X-ray photoelectron and conversion spectra of this oxide [13,14].…”

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Nature of the Chemical Bond in Uranium Dioxide UO2

et al. 2005

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Fine structure of the X-ray photoelectron and conversion spectra of low-energy (0 3 40 eV) electrons of uranium dioxide UO 2 was analyzed based on the electronic structure calculations for the UO 8 12! cluster with O h symmetry, simulating the nearest surrounding of uranium in UO 2 , by the relativistic X = discrete variation method. It was predicted theoretically and validated experimentally that, in UO 2 , the U5f electrons (~1 U5f electron) can directly participate in chemical bonding:~2 U5f electrons weakly contributing to chemical bonding are localized at 31.9 eV;~1 U5f electron participating in chemical bonding is delocalized in the range of outer valence molecular orbital energies from 3 4 to 39 eV; and unfilled U5f states are localized mostly at low (from 0 to 5 eV above zero) energies. It was shown experimentally that the U6p electrons actively participate in formation of not only inner valence but also outer valence (0.6 U6p electron) molecular orbitals. The density of the U6p states in UO 2 was estimated experimentally. The composition and sequence of the inner valence molecular orbitals at energies within 133 40 eV were also elucidated.X-ray photoelectron spectroscopic (XPS) studies of uranium oxides showed that the spectra of low-energy electrons in UO 2 and UO 3 at binding energies E b within 0 3 40 eV markedly differ in the structure [13 4]. The U(VI) ion in the trioxide UO 3 has the electronic configuration {Rn}5f 0 , and the U(IV) ion in the dioxide UO 2 , the {Rn}5f 2 configuration (where {Rn} is the electronic configuration of radon), and the X-ray photoelectron spectrum of UO 2 , by contrast to UO 3 , exhibits at ³E b ³ = 1.9 eV a fairly narrow intense line of U5f electrons weakly contributing to the chemical bonding.Also, at low binding energies (within 0 3 40 eV) of electrons of uranium oxides and other actinide compounds, the lines observed have, for the most part, a width of several electron-volts. This is in many cases larger than the width of the lines of electrons from deeper-lying inner shells [5]. For example, the half-width G, eV, of the line of the O1s electrons (³E b ³ = 530.5 eV) of UO 2 was estimated at 1.6 eV, while that of the O2s electrons (³E b ³ = 23.3 eV), at 4 eV, and this line has a fine structure [3,4]. These data contradict the indeterminacy relationship DEDth /2p, where DE is the natural width of the level from which a photoelectron was removed; Dt, lifetime of the hole state of the ion formed; and h, Planck's constant. Indeed, the lifetime of the hole Dt tends to decrease with increasing absolute value of the level energy, and the lines in the X-ray photoelectron spectra of separate atoms should become narrower with decreasing binding energy of the electrons. In the case of UO 2 and UO 3 , the situation is the opposite. This stimulated extensive theoretical and experimental studies on the nature of the chemical bonding in actinide compounds. These studies showed that one reason for broadening of the lines in the X-ray photoelectron spectra in the region of low binding...

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Nature of the Chemical Bond in Uranium Dioxide UO2

et al. 2005

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“…The XPS from γ-UO 3 not containing the U 5f electrons does not exhibit this peak. 61 Since the U 5f BE is about ~3 eV lower than that of the low energy OVMO band edge ("quasi-gap"), one can suggest that the U 5f intensity must decrease discretely as uranium oxidation state grows from U 4+ to U 5+ and U 6+ , since the U 5f electrons transit from the localized state to the outer valence band. The U 5f intensity must first decrease twice and then vanish (Figure 3).…”

Section: Figurementioning

confidence: 99%

“…17,50,59 The binding energy (BE) E b (U 4f 7/2 ) of the U 4f 7/2 electrons in uranium and oxides grows as: ~377 eV (metallic U); ~380 eV (U 4+ ); ~381 eV (U 5+ ); ~382 eV (U 6+ ). 17,50,55,56,59,60,61,62 A special attention was paid to the study of mechanisms of structure formation, which leads to widening of main peaks and appearance of extra structure in the spectra. 50,59,63 The XPS spectra of some oxides exhibit typical shake-up satellites of about ~25% intensity of the basic peaks 41,51,60,64 The calculated spectroscopic factors f Anf reflecting the fractions of the basic peak XPS intensities with the deduction of shake-up satellite intensities for the U 4f and U 5f peaks are: f U4f =0.83 and f U5f =0.86.…”

Section: Introductionmentioning

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XPS Study of Ion Irradiated and Unirradiated UO₂ Thin Films

et al. 2016

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XPS determination of the oxygen coefficient k O =2+x and ionic (U 4+ , U 5+ and U 6+ ) composition of oxides UO 2+x formed on the surfaces of differently oriented (hkl) planes of thin UO 2 films on LSAT (Al 10 La 3 O 51 Sr 14 Ta 7 ) 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 UO 2+x on the surface with mean oxygen coefficients k O 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 k O 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 k O values. The observed difference in the k O values, 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 UO 2 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 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.3

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“…The latter method is used to determine the physicochemical state of radionuclides in the environment. Reduction of Cr(VI) to Cr(III) on the goethite surface by Fe(II) traces [6] and interaction of uranyl with calcite and diabase [7] were studied by XPS previously.…”

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An XPS study of interaction of neptunyl(V) in aqueous solution with goethite (?-FeOOH)

et al. 2004

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Sorption and physicochemical state of Np on the goethite (a-FeOOH) surface were studied.The oxidation state of Np on the a-FeOOH surface was studied by the liquid extraction. The neptunium complexes formed on the surface were studied by X-ray photoelectron spectroscopy. The ionic and elemental composition of the goethite surface and NpO 2 + complexes with a-FeOOH were determined from the XPS data.No Np(IV) and Np(VI) compounds were detected. Neptunyl(V) Np(V)O 2 + forms complexes with the surface groups of a-FeOOH. The equatorial plane of these complexes is occupied by the oxygen atoms of a-FeOOH and water and/or carbonate group CO 3 2! .Migration, bioavailability, and hence toxicity of radionuclides depend on their physicochemical state in the environment [1]. The mobility of radionuclides is essentially determined by processes occurring on the mineral3natural water interface (sorption, redox reactions) and types of radionuclide complexes formed on the surface of minerals and suspended particles. Neptunium mainly occurs in nature in the form of neptunyl(V) ion NpO 2 + . This is a linear dioxo cation with the formal charge of +1. Since the electron density on the central atom is low, NpO 2 + is relatively inert chemically and hence readily migrates in the environment. Under these conditions, it can be reduced to Np(IV) or oxidized to Np(VI)O 2Goethite is an abundant iron-containing mineral having high sorption capacity for heavy metal ions and radionuclides [335]. In this work we studied sorption of Np(V)O 2 + on the goethite (a-FeOOH) surface and the surface complexes of neptunyl(V) by both liquid3liquid extraction allowing separation of neptunium species in different oxidation states and by X-ray photoelectron spectroscopy (XPS). The latter method is used to determine the physicochemical state of radionuclides in the environment. Reduction of Cr(VI) to Cr(III) on the goethite surface by Fe(II) traces [6] and interaction of uranyl with calcite and diabase [7] were studied by XPS previously. EXPERIMENTALGoethite (a-FeOOH, sample I) was prepared by the procedure in [8]. Fe(NO 3 ) 3 . 9H 2 O (50 g, chemically pure grade) was dissolved in double-distilled water (825 ml). A 2.5 M KOH solution (200 ml) was added. The resulting solution was heated at 60oC for 24 h with continuous stirring. The precipitate was washed several times with double-distilled water and acetone and dried at 40oC for 2 days. For sorption experiments, an a-FeOOH suspension was prepared.Sample II was prepared as follows. A goethite suspension (0.0374 g of sample I with 1.6 0 10 18 nm 2 free surface area of the mineral and 5.2 0 10 36 mol of the sorption centers) was placed in a centrifugation tube, and a supporting electrolyte (0.1 M NaClO 4 ) was added. Then 237 Np(V) was added in an amount corresponding to approximately 10 36 M total Np concentration. The pH was adjusted at 7.2 + 0.2, and the solution was continuously stirred for several days. The mother liquor was separated by centrifugation at 6000 rpm. After that, an aliquot of the mother liq...

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Cited by 16 publications

References 9 publications

Nature of the Chemical Bond in Uranium Dioxide UO2

Nature of the Chemical Bond in Uranium Dioxide UO2

XPS Study of Ion Irradiated and Unirradiated UO₂ Thin Films

An XPS study of interaction of neptunyl(V) in aqueous solution with goethite (?-FeOOH)

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Untitled

Cited by 16 publications

References 9 publications

Nature of the Chemical Bond in Uranium Dioxide UO2

Nature of the Chemical Bond in Uranium Dioxide UO2

XPS Study of Ion Irradiated and Unirradiated UO2 Thin Films

An XPS study of interaction of neptunyl(V) in aqueous solution with goethite (?-FeOOH)

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XPS Study of Ion Irradiated and Unirradiated UO₂ Thin Films