Covalency in oxidized uranium

Tobin, J. G.; Yu, Shou-Wen; Qiao, Ruimin; Yang, Wanli; Booth, C. H.; Shuh, David K.; Duffin, Andrew M.; Sokaras, Dimosthenis; Nordlund, Dennis; Weng, Tsu Chien

doi:10.1103/physrevb.92.045130

Cited by 26 publications

(39 citation statements)

References 25 publications

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“…Instead, when the CFS are neglected, the total number of Mott localized 5f electrons is 1.98, while the occupation of the extended 5f degrees of freedom is only 0.16. The fact that the overall occupancy of the 5f levels deviates considerably from an integer value confirms the importance of covalency effects in UO 2 , which has been pointed out also in previous experimental and theoretical studies [46][47][48][49]. Note also that the Mott-localized Γ 8 degrees of freedom have occupancy close to integer, which is a factor that is known to promote localization [3].…”

supporting

confidence: 59%

“…By utilizing our theoretical approach, we have performed first principle calculations of the orbitalselective Mott insulator UO 2 , finding good agreement with available experimental data. Furthermore, we have demonstrated that taking into account the CFS is essen-tial in order to capture the correct pattern of orbital differentiation between the U-5f states, and that the main physical reason underlying the CFS orbital differentiation in UO 2 is not the contribution of the crystal field on-site energies (which is essentially negligible), but concerns the hybridization between the U-5f and the O-2p electrons [37], which originates covalent bonds in this material [46][47][48][49]. The strong orbital differentiation between the Γ 8 and the Γ 7 electrons could be directly detected experimentally, e.g., by means of angle-resolved photoemission techniques [50,51], which would enable us to discriminate between the spectral contributions of the different states based on their symmetry properties.…”

mentioning

confidence: 99%

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Slave Boson Theory of Orbital Differentiation with Crystal Field Effects: Application toUO2

Lanatà¹,

Yao²,

Deng

et al. 2017

Phys. Rev. Lett.

105

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We derive an exact operatorial reformulation of the rotational invariant slave boson method and we apply it to describe the orbital differentiation in strongly correlated electron systems starting from first principles. The approach enables us to treat strong electron correlations, spin-orbit coupling and crystal field splittings on the same footing by exploiting the gauge invariance of the mean-field equations. We apply our theory to the archetypical nuclear fuel UO2, and show that the ground state of this system displays a pronounced orbital differention within the 5f manifold, with Mott localized Γ8 and extended Γ7 electrons.

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supporting

confidence: 59%

mentioning

confidence: 99%

Slave Boson Theory of Orbital Differentiation with Crystal Field Effects: Application toUO2

Lanatà¹,

Yao²,

Deng

et al. 2017

Phys. Rev. Lett.

105

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“…However, the lifetime broadening of the 3d core holes (several eV) dominates the spectral widths. The sample used was the same as used in earlier studies [2,3]. Uranium samples can be affected by oxidation and sample corruption, but these were not a problem here, as described earlier [30].…”

Section: Methodsmentioning

confidence: 99%

“…X-ray spectroscopy has become a powerful tool for the analysis of the electronic structure of actinides, [1][2][3][4][5][6][7][8][9][10][11][12], based upon the original ground breaking work of (1) Veal and coworkers using X-ray Photoelectron Spectroscopy (XPS) [13][14][15][16]; (2) Naegele and others employing the lower energy Photoelectron Spectroscopy (PES) [17] and references therein; (3) Baer et al utilizing Bremstrahlung Isochromat Spectroscopy (BIS) [18,19]; (4) Chauvet and Baptist, with the lower energy Inverse Photoelectron Spectroscopy (IPES) [20]; and Kalkowski, Kaindl, Brewer and Krone, who did a pioneering X-ray Absorption Spectroscopy (XAS) study [21].…”

Section: Introductionmentioning

confidence: 99%

Towards the Quantification of 5f Delocalization

Tobin

Nowak

et al. 2020

Applied Sciences

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By using M4,5 X-ray Emission Spectroscopy (XES) in the tender X-ray regime, it is possible to quantify 5f delocalization in the actinides. Previous analyses, utilizing the Branching Ratio (BR) in the N4,5 X-ray Absorption Spectroscopy (XAS), could not discriminate between the cases of localized n = 2 and delocalized n = 3, in uranium materials, where n is the number of 5f electrons on the U entity. Here, it is shown that, by employing the ubiquitous 6p → 3d XES as a point of normalization, the localized n = 2 and delocalized n = 3 cases can be easily distinguished and quantified.

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“…The lower energy peak is of predominantly U 5f character, and is well separated and distinct from a higher energy peak that is predominantly of U 6d character. [36][37][38] The energies of these peaks are ~533.5 eV and ~538-540 eV, with those of U(IV) higher than U(VI) by, respectively, ~0.5 and ~1.5 eV. The valley between these peaks decreases with increasing valence by ~1.5 eV, but in a more complicated way because of variations in the peak widths and the presence of additional spectral features.…”

Section: A O Xas and Rixs Of Relevant Standard Compoundsmentioning

confidence: 97%

Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in UO2+x

Conradson¹,

Andersson²,

Boland³

et al. 2017

Phys. Rev. B

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with O XAS and NIXS and U M 5 RIXS shows that O-doping raises the peak of the U 5f states of the valence band by ~0.4 eV relative to a calculated value of 0.25 eV. However, it lowers the edge of the conduction band by 1.5 eV vs. the calculated 0.6 eV, a difference much larger than the experimental error. This 1.9 eV reduction in the gap width constitutes most of the 2-2.2 eV gap measured by optical absorption. In addition, the XAS spectra show a tail that will intersect the occupied U 5f states and give a continuous density-of-states that increases rapidly above its constricted intersection. Femtosecond-resolved photoemission measurements of UO 2 coincident with the excitation pulse with 4.7 eV excitation show the unoccupied 5f states of UO 2 and no hot electrons. 3.1 eV excitation, however, complements the Odoping results by giving a continuous population of electrons for several eV above the Fermi level. The CPQP in photoexcited UO 2 therefore fulfills the criteria prescribed for a non-equilibrium condensate. The electron distributions resulting from both excitations persist for 5-10 ps, indicating that they are the final state that therefore forms without passing through the initial continuous distribution of nonthermal electrons observed for other materials. Three exceptional findings are: 1) the direct formation of both of these long lived (>3-10 ps) excited states without the short lived nonthermal intermediate; 2) the superthermal metallic state is as or more stable than typical photoinduced metallic phases; and 3) the absence of hot electrons accompanying the insulating UO 2 excited state. This heterogeneous, non-equilibrium, Fröhlich BEC stabilized by a FanoFeshbach resonance therefore continues to exhibit unique properties.Closing the Mott gap in UO 2(+x) -2

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Covalency in oxidized uranium

Cited by 26 publications

References 25 publications

Slave Boson Theory of Orbital Differentiation with Crystal Field Effects: Application toUO2

Slave Boson Theory of Orbital Differentiation with Crystal Field Effects: Application toUO2

Towards the Quantification of 5f Delocalization

Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in UO2+x

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