The structure of X-ray photoelectron spectra of light actinide compounds

Teterin, Yurii A.; Teterin, A. Yu.

doi:10.1070/rc2004v073n06abeh000821

Cited by 76 publications

(128 citation statements)

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“…To conclude, we also carried out such complex studies for other compounds of actinides and reported the results in part in [3].…”

Section: Resonance X-ray O 4 5 (U) Emission Spectroscopy (Rxes)mentioning

confidence: 89%

“…The structure of this spectrum was qualitatively identified on the basis of the characteristics of the X-ray photoelectron spectrum of UO 2 , using the OVMO and IVMO concept [3,4]. Our results suggest that the spectral characteristics can also serve as a quantitative measure of the validity of the electronic structure calculations for UO 2 [9].…”

Section: Conversion Electron Spectroscopy (Ces)mentioning

confidence: 91%

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X-Ray Spectral Methods in Investigation of the UO2 Electronic Structure

Teterin

2005

Radiochemistry

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Fine structure of the X-ray photoelectron spectrum of UO 2 at electron binding energies from 0 tõ 40 eV is primarily due to electrons of outer (0 315 eV) and inner (153 40 eV) valence molecular orbitals formed from unoccupied U5f,6d,7s and O2p and occupied low-energy U6p and O2s shells of the neighboring uranium and oxygen atoms, respectively. This is consistent with the results of the relativistic calculation of the electronic structure of the UO 8 12! cluster with O h symmetry, simulating the nearest surrounding of uranium in UO 2 , and is confirmed by the data of X-ray spectroscopy (conversion electron, nonresonance and resonance X-ray O 4, 5 (U) emission, O 4, 5 (U) XANES, photoelectron resonance, and Auger spectroscopy of oxygen). The fine structure of the X-ray photoelectron spectra, associated with electrons from outer valence and inner valence molecular orbitals, allows estimation of the degree of participation of U6p,5f electrons in chemical bonding, as well as the structure of the nearest surrounding of the uranium atom and the bond length in its oxides. The total contribution from electrons of inner valence molecular orbitals to the absolute value of the chemical bonding energy can be compared with the corresponding contribution of the electrons from outer valence molecular orbitals to bonding of the atoms. Inner valence molecular orbitals can be formed in compounds of any elements, and this is an important new fact in chemistry and physics of condensed state.It was traditionally believed that chemical bonds in compounds are formed mostly from electrons of unoccupied low-energy (from 0 to~15 eV) shells of the neighboring atoms. This was favored to a certain extent by a wide use of sources of excitation in the visible and UV regions in spectroscopy of atoms and molecules. X-ray emission spectroscopic studies of various substances were also oriented mostly at these electron energy regions. Although participation of electrons from relatively deep-lying occupied atomic shells (from~15 to~50 eV) in formation of inner valence molecular orbitals (IVMOs) is justified from the quantum-mechanical viewpoint, it was believed that their influence on the interatomic bonds in compounds is negligible compared to the most weakly bound electrons of the outer valence molecular orbitals (OVMOs) (energies from 0 to~15 eV). However, we found recently [133] that, under certain conditions, inner valence molecular orbitals can be formed in compounds of any elements [133]. This is a new, extremely important, scientific fact in chemistry and physics of condensed state, which can hardly be overestimated.In this study, we consider new data on the nature of chemical bonding with UO 2 as an example. These data were obtained using modern X-ray spectral methods such as X-ray photoelectron, conversion electron, nonresonance and resonance X-ray O 4, 5 (U) emission, O 4, 5 (U) XANES, photoelectron resonance, and Auger spectroscopy of oxygen, taking into account the results of the relativistic calculation of the electronic structure of th...

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“…To conclude, we also carried out such complex studies for other compounds of actinides and reported the results in part in [3].…”

Section: Resonance X-ray O 4 5 (U) Emission Spectroscopy (Rxes)mentioning

confidence: 89%

Section: Conversion Electron Spectroscopy (Ces)mentioning

confidence: 91%

X-Ray Spectral Methods in Investigation of the UO2 Electronic Structure

Teterin

2005

Radiochemistry

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“…The structure observed in the second region, from 13 to 50 eV, is associated with electrons of inner valence molecular orbitals (IVMOs). The characteristics of this pattern reflect the structure of the nearest surrounding of the ion in the compound, and for actinide phases they can be used for determining the bond lengths between the actinide atom and the nearest O atoms [2]. Because the pattern under consideration reflects the total density of states of valence electrons, taking into account their photoemission cross sections, it can serve as a criterion of the correctness The pattern observed in the region of electron binding energies higher than 50 eV may be due, to a small extent, to electrons of inner (core) molecular orbitals (CMOs).…”

Section: Resultsmentioning

confidence: 99%

“…X-ray photoelectron spectroscopy (XPES) allows studying the chemical state of elements on the surface of ceramic matrices. Conclusions on the oxidation state of actinides can be made both from the binding energies of inner electrons and from the characteristics of the fine structure of their XPE spectra [2]. Previously we studied by XPES borosilicate glasses with U [3] and pyrochlore ceramics containing Се and Th [4].…”

mentioning

confidence: 99%

X-ray photoelectron study of murataite ceramics containing Th, U, Np, and Pu

Maslakov

Teterin

et al. 2012

Radiochemistry

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The structure of X-ray photoelectron spectra of actinide-containing (An = Th, U, Np, and Pu) murataite ceramic (Ti-Mn-Ca-An-Zr-Al-Fe-O) samples as potential matrices for immobilization of actinide radioactive waste was studied. The elemental composition of the sample surface was analyzed, and comparison with the calculated data for the bulk of the samples was made. The binding energies of the An4f electrons and the parameters of the fine structure of their X-ray photoelectron spectra were determined. These parameters were compared with the corresponding values for the dioxides.The environmentally safest way of high-level waste (HLW) isolation is their vitrification or ceramization followed by disposal in geological repositories. For HLW immobilization, it is suggested to use aluminum phosphate and borosilicate glasses [1]. Unfortunately, they crystallize with time, which leads to an increase in their solubility in water. To decrease the volume and enhance the reliability of HLW storage, it is appropriate to perform partitioning with the separation of actinide elements, which are the most long-lived and radiotoxic. Correspondingly, it is necessary to incorporate the actinide fraction into a special ceramic based on chemically stable and radiation-resistant phases. The development of stable matrices for actinide waste immobilization is an important scientific and practical problem. Therefore, it is an urgent problem to reveal phases with high capacity for actinides and other HLW components, to determine the oxidation state and coordination of radionuclide cations in them, and to analyze the stability of the structure of phases on the surface of the ceramic matrix [1].To understand processes that occur in matrices in storage, it is necessary to know the physicochemical forms (ionic composition, oxidation state of elements, structure of the nearest surrounding) of radionuclides in them. X-ray photoelectron spectroscopy (XPES) allows studying the chemical state of elements on the surface of ceramic matrices. Conclusions on the oxidation state of actinides can be made both from the binding energies of inner electrons and from the characteristics of the fine structure of their XPE spectra [2]. Previously we studied by XPES borosilicate glasses with U [3] and pyrochlore ceramics containing Се and Th [4]. In this study, we examined by this method the surface of a ceramic of the elemental composition TiMn-Ca-An-Zr-Al-Fe-O with the murataite structure, containing actinides (An = Th, U, Np, and Pu), with the aim to determine the oxidation state of actinides and changes in the elemental composition of the surface compared to the bulk. This is necessary for predicting the stability of such ceramic in prolonged storage.

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“…For the modeling of boundary conditions we used an "extended cluster" scheme described in details in Refs. [20,21]. In this model the crystal fragment under study consists of two parts: the internal main part (or the "core" of the cluster) and the outer part (or the "shell").…”

Section: I3 Electronic Structure Calculations For Pu 19mentioning

confidence: 99%

Contract B590089: Technical Evaluation of the Pu Cluster Calculations

Tobin¹,

Ryzhkov²,

Mirmelstein³

2011

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Contract B590089: Technical Evaluation of the Pu Cluster CalculationsTobin, LLNL Page 18 November 2011 2Comparison 1: X--ray Photoelectron Spectroscopy (XPS), Bremstrahlung Isochromat Spectroscopy (BIS), also known as Inverse Photoelectron Spectroscopy (IPES), and X--ray Absorption Spectroscopy (XAS) versus cluster calculation results for UO2.The experimental results (bottom) are from References 1 and 2 and the theoretical results (top) are from Appendix C. This is very promising. Because we inserted a band--gap of 2.1 eV artificially, the density of states (DOS) calculations have been split at the energy zero and aligned with the valence band maximum (VBM) in the XPS and the Conduction Band Minimum (CBM) in the BIS and XAS. UDOS is the unoccupied density of states. ODOS is the occupied density of states. While others have already made such comparisons with XPS and the ODOS [Y.A. Teterin and A.Y. Teterin, Russian Chemical Reviews 73, 541 (2004)], this is the first such definitive comparison of the ODOS with the BIS and XAS. In general, there is strong agreement in terms of the U6d, U5f, and O2p DOS with the spectral features. Contract B590089: Technical Evaluation of the Pu Cluster CalculationsTobin, LLNL Page 18 November 2011 3Comparison 2: Synchrotron--Radiation--based Photoelectron Spectroscopy (PES) versus cluster calculation results for PuO2.The experimental results (top) are from Reference 3 and the theoretical results (bottom) are from Appendix C. This Pu spectrum are from an alpha--Pu sample with a delta--Pu surface reconstruction. By working at the Cooper Minimum, the relative intensity of the Pu 5f can be diminished and the contribution of the other peaks amplified. Clearly, there is once again strong agreement between the ODOS for the Pu5f, O2p, Pu6p3/2, O2s, and Pu6p1/2 and the corresponding spectroscopic features. Contract B590089: Technical Evaluation of the Pu Cluster CalculationsTobin, LLNL Page 18 November 2011 4Comparison 3: Synchrotron--Radiation--based Photoelectron Spectroscopy (PES) versus cluster calculation results for Pu.The experimental results (bottom) are from Reference 3 and the theoretical results (top) are from Appendix B. These Pu spectra are from an alpha--Pu sample with a delta--Pu surface reconstruction. The calculations once again provide a meaningful simulation of the observed states: Pu5f, Pu6d, Pu6p3/2 and Pu6p1/2. By tuning the photon energy, different states can be emphasized and de--emphasized. At the anti--resonance, hv = 100 eV, the Fermi Edge step should be representative of the Pu 6d states. On Resonance, hv = 125 eV, the Fermi Edge should be dominated by the Pu5f states. Despite the small amount of oxidation, these spectra should provide accurate basis for comparison with bulk, metallic Pu. Contract B590089: Technical Evaluation of the Pu Cluster CalculationsTobin, LLNL Page 18 November 2011 5Comparison 4: 5f occupations. One of the crucial issues in Pu electronic structure is that of the differentiation of the 6d and 5f states. Where are the Pu5f and Pu 6d states?...

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The structure of X-ray photoelectron spectra of light actinide compounds

Cited by 76 publications

References 84 publications

X-Ray Spectral Methods in Investigation of the UO2 Electronic Structure

X-Ray Spectral Methods in Investigation of the UO2 Electronic Structure

X-ray photoelectron study of murataite ceramics containing Th, U, Np, and Pu

Contract B590089: Technical Evaluation of the Pu Cluster Calculations

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