Formation and stability of actinide oxides: a valence band photoemission study

Seibert, Α.; Gouder, T.; Huber, F.

doi:10.1524/ract.2009.1605

Cited by 15 publications

(10 citation statements)

References 13 publications

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“…The O 2p band changed its shape from the double peak appearance to a much more symmetric shape with a maximum at higher BE compared to the original PuO 2 surface. The spectrum now is more similar to that of Pu 2 O 3 than PuO 2 [25,34]. An identification of these uppermost surface species as mainly Pu 2 O 3 with in some cases an admixture of PuO 2 and with additional H 2 O/OH features (eg.…”

Section: High Ice Dosagementioning

confidence: 79%

Interaction of PuO₂thin films with water

Seibert¹,

Gouder

Huber

2010

Ract

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Plutonium dioxide / Water / Reduction / Photochemistry / Photoelectron spectroscopySummary. The surface adsorption and reaction of water with PuO 2 thin films was investigated by X-ray and ultra-violet photoelectron spectroscopies (XPS and UPS, respectively). Initial motivation of the work was to further investigate the potential role of water in promoting the surface oxidation of PuO 2 to Pu(IV)/Pu(V) mixed oxides formerly discussed in literature which may seriously impede the stability of spent nuclear fuel. Water may act as oxidant, as catalyst for the oxidation by O 2 , or as reactant leading to formation of hydrous oxide being oxidized by O 2 instead of PuO 2 (cr). In order to obtain high water coverage under the experimentally required ultra-high vacuum conditions, water was adsorbed at low temperature (77 K) as thick ice film. Results were compared to thin water layers adsorbed at room temperature.When adsorbed at 298 K, water dissociates forming a thin hydroxyl (OH − ) layer with small amounts of molecularly adsorbed water but no further reaction (in the sense of oxidation or reduction) is detected. At 77 K, water condenses as ice film. Here, a mainly non-dissociative adsorption of water is observed for layers ∼ 1 ML while for higher dosages, only molecular water/ice is observed and no significant contribution of OH (in the water layers) is detected. When exposing the sample to UV light while warming it up, the ice layer thaws and desorbs leaving behind a Pu 2 O 3 surface. This surprising reduction of PuO 2 stands in sharp contrast to the radiolytically driven oxidation of spent fuel in presence of water. It is discussed in terms of a photochemically driven interface reaction.

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Section: High Ice Dosagementioning

confidence: 79%

Interaction of PuO₂thin films with water

Seibert¹,

Gouder

Huber

2010

Ract

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“…Adsorption energies of water on differently oriented uranium dioxide planes were calculated. 14, 15,16 The work on the study of the electronic structure of uranium and its alloys [17][18][19][20][21] and oxides UO 2+x (x≤0 and x≥0) employed theoretical calculation results, [22][23][24][25][26][27][28][29][30][31][32][33][34] photoelectron spectroscopy (PES) [35][36][37][38][39][40][41] and X-ray photoelectron spectroscopy (XPS) widely. 38,[42][43][44][45][46][47][48][49][50][51][52][53][54][55] These techniques were used to study films on various substrates.…”

Section: Introductionmentioning

confidence: 99%

“…The work on the study of the electronic structure of uranium and its alloys − and oxides UO 2+ x ( x ≤ 0 and x ≥ 0) employed theoretical calculation results, − photoelectron spectroscopy (PES), − and X-ray photoelectron spectroscopy (XPS) widely. ,− These techniques were used to study films on various substrates. − ,− …”

Section: Introductionmentioning

confidence: 99%

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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“…A lot of attention has been focused on theoretical studies of uranium dioxide's electronic structure . Studies of the valence electronic states in UO 2 employ photoelectron (PES) and X‐ray photoelectron spectroscopy (XPS) . Auger O KLL spectrum, O 4,5 (U)‐edge resonant emission spectra, nonresonant and resonant O 4,5 (U) emission spectra, valence electron conversion spectra (CES), X‐ray absorption spectra (XAS), and resonant inversion photoelectron spectra of UO 2 have been studied previously.…”

Section: Introductionmentioning

confidence: 99%

The nature of the chemical bond in UO₂

Maslakov

Teterin

Ryzhkov

et al. 2019

Int J of Quantum Chemistry

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The nature of the chemical bond in UO2 was analyzed taking into account the X‐ray photoelectron spectroscopy (XPS) structure parameters of the valence and core electrons, as well as the relativistic discrete variation electronic structure calculation results for this oxide. The ionic/covalent nature of the chemical bond was determined for the UO8 (D4h) cluster, reflecting uranium's close environment in UO2, and the U13O56 and U63O216 clusters, reflecting the bulk of solid uranium dioxide. The bar graph of the theoretical valence band (from 0 to ~35 eV) of XPS spectrum was built such that it was in satisfactory agreement with the experimental spectrum of a UO2 single crystalline thin film. It was shown that unlike the crystal field theory results, the covalence effects in UO2 are significant due to the strong overlap of the U 6p and U 5f atomic orbitals with the ligand orbitals, in addition to the U 6d atomic orbital (AO). A quantitative molecular orbital (MO) scheme for UO2 was built. The contribution of the MO electrons to the chemical bond covalence component was evaluated on the basis of the bond population values. It was found that the electrons of inner valence molecular orbitals (IVMO) weaken the chemical bond formed by the electrons of outer valence molecular orbitals (OVMO) by 32% in UO8 and by 25% in U63O216.

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Formation and stability of actinide oxides: a valence band photoemission study

Cited by 15 publications

References 13 publications

Interaction of PuO₂thin films with water

Interaction of PuO₂thin films with water

XPS Study of Ion Irradiated and Unirradiated UO₂ Thin Films

The nature of the chemical bond in UO₂

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Formation and stability of actinide oxides: a valence band photoemission study

Cited by 15 publications

References 13 publications

Interaction of PuO2thin films with water

Interaction of PuO2thin films with water

XPS Study of Ion Irradiated and Unirradiated UO2 Thin Films

The nature of the chemical bond in UO2

Contact Info

Product

Resources

About

Interaction of PuO₂thin films with water

Interaction of PuO₂thin films with water

XPS Study of Ion Irradiated and Unirradiated UO₂ Thin Films

The nature of the chemical bond in UO₂