Thermal variation of the optical absorption of UO2: determination of the small polaron self-energy

Ruello, P.; Becker, Klaus‐Dieter; Ullrich, K.; Desgranges, Lionel; Petot, C.; Petot-Ervas, G.

doi:10.1016/j.jnucmat.2004.03.002

Cited by 46 publications

(24 citation statements)

References 39 publications

(138 reference statements)

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“…They must therefore originate in some other factor that would be unique to the mixed valence fluorite compounds. Small or unaggregated, localized polarons 75 as have been proposed to be thermally activated in UO 2 75 -or possibly promoted by pressure that lowers their formation energy 86 -contract the band gap by amounts close to those calculated for U 4 O 9 and U 3 O 7 . These amounts are, however, much less than the values found in the XAS.…”

Section: Rixs O Xas and Nixs Measurements Of U 4 O 9 And U 3 Omentioning

confidence: 54%

“…31,33,36 The optical gap of ~2 to ~2.4 eV is slightly on the high side but within the error of the measurements. 75,76 In addition to the assignment of the features, extended analyses of UO 2 show that the width and complexity of the peaks of its spectrum are the result of a combination of crystal field, Coulomb, and multiplet splitting effects (SI and Fig. S3).…”

Section: A O Xas and Rixs Of Relevant Standard Compoundsmentioning

confidence: 99%

“…The behavior of the gap inferred from this combination of RIXS and XAS can be compared with direct optical absorption measurements of UO 2 at high temperature 75 or pressure. 86 Such a comparison demonstrates that these novel states are not the postulated small polarons that reside in the slightly modified structures 78,99,100 found by neutron scattering [79][80][81][82][83][84] or the result of similar small compressions of the U-O bonds.…”

Section: E Dos Of the Coherent Quantum Phase Of Photoinduced Polaronsmentioning

confidence: 99%

See 2 more Smart Citations

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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Section: Rixs O Xas and Nixs Measurements Of U 4 O 9 And U 3 Omentioning

confidence: 54%

Section: A O Xas and Rixs Of Relevant Standard Compoundsmentioning

confidence: 99%

Section: E Dos Of the Coherent Quantum Phase Of Photoinduced Polaronsmentioning

confidence: 99%

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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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show abstract

“…It is sufficient to consider this particle of corium as opaque particle in the near-infrared. More recent study by Ruello et al [55] on spectral absorption of UO 2 in the temperature range from room temperature up to 1173 K confirmed the high absorption in the visible and near-infrared. It was also shown in [55] that the boundary of the strong optical absorption band moves to the infrared range when the sample is heated.…”

Section: Optical Propertiesmentioning

confidence: 77%

“…More recent study by Ruello et al [55] on spectral absorption of UO 2 in the temperature range from room temperature up to 1173 K confirmed the high absorption in the visible and near-infrared. It was also shown in [55] that the boundary of the strong optical absorption band moves to the infrared range when the sample is heated. One can use an approximate model of totally opaque gray particle in simplified heat transfer calculations for corium particles.…”

Section: Optical Propertiesmentioning

confidence: 77%

Steam explosion in nuclear reactors: Droplets of molten steel vs core melt droplets

Dombrovsky

2017

International Journal of Heat and Mass Transfer

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Synthesis of Air‐Stable, Volatile Uranium(IV) and (VI) Compounds and Their Gas‐Phase Conversion To Uranium Oxide Films

et al. 2014

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Thermal variation of the optical absorption of UO2: determination of the small polaron self-energy

Cited by 46 publications

References 39 publications

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

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

Steam explosion in nuclear reactors: Droplets of molten steel vs core melt droplets

Synthesis of Air‐Stable, Volatile Uranium(IV) and (VI) Compounds and Their Gas‐Phase Conversion To Uranium Oxide Films

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