Optical properties and electronic structure of UO2

Abstract

The near normal incidence reflectivity of UO2 single crystals has been measured in the photon energy range from 0.03 eV to 13 eV. From the reflectivity spectrum the complex dielectric function ε (ω) =ε1(ω)+iε2(ω) has been derived by means of the Kramers-Kronig relation. In addition the absorption coefficient was determined from a direct transmission measurement on thin single crystal plates in the weakly absorbing spectral region below the absorption edge. An energy level scheme is proposed which allows a self-consistent assignment of the structure in ε2 with optical transitions between maxima in the density of states. The energy gap found at 2.1±0.1 eV is attributed to a 5f2→5f16deg transition. A crystal field splitting 10Dq=2.8 eV is derived for the 6d conduction states. Good agreement is obtained within this model with XPS measurements and a recent molecular cluster approximation. It disagrees with a previous interpretation of reflectivity data.

First-principles study of water adsorption and dissociation on the UO2 (1 1 1), (1 1 0) and (1 0 0) surfaces

“…Following the work by Dudarev et al, Yun et al [18,19] performed a DFT+U calculation (U = 4.50 eV and J = 0.50 eV) on the antiferromagnetic ground state of UO 2 . Similar DFT+U calculations (U = 4.772eV and J = 0.511 eV) by Yu et al [20] obtained a band gap of 2.1 eV, which is consistent with the experimental value [2]. All these calculations indicated that the DFT+U method has been successfully applied to study the properties of uranium dioxide.…”

“…Owing to its technological relevance in the nuclear power industry and its significance from fundamental scientific point of view, uranium dioxide is intensely studied both experimentally [1][2][3][4][5] and theoretically [6][7][8]. One of the challenging research topics about uranium dioxide is the reactions of uranium dioxide with water, which it is associated with many fundamental phenomena related to hydrogen production [9,10], corrosion [11] and modifications of crystal morphologies [12,13].…”

Uranium Oxide Nanocrystals by Microwave‐Assisted Thermal Decomposition: Electronic and Structural Properties

“…[27] The band maximum at 218 nm corresponds to the 5f 2 Ǟ 6dt 2g 5f 1 transition, while the lower energy band can be assigned to the 5f 2 Ǟ 6de g 5f 1 transition with a shoulder from spin orbit splitting. [28] However, DEG also exhibits an absorption band with a maximum at ca. 325 nm.…”

“…8 eV). [28] Whereas the oxygen K-edge XAS measurements suggest a f-f type band transition, the optical spectra propose that UO 2 is a f-d type since upon excitation neither the O 2p nor the U 5f electrons can access the unoccupied 5f state but only the unoccupied 6d state according to dipole selection rules. [29] The bandgap of the material was determined using the Tauc formula for direct bandgap materials.…”

Absorption of optical radiation by nanoclusters of sputtered metallic uranium and its oxides

“…Consequently, the sputtering of thin-film coatings of laser elements based on metallic uranium can strongly affect laser media which use photodissociation under the action of the radiation from inert-gas excimers for pumping. The optical properties of uranium dioxide UO 2 have been studied in [13]. Uranium dioxide is transparent in the range ˙ω < 2 eV.…”