Optical band gap of NpO2 and PuO2 from optical absorbance of epitaxial films

Abstract

We report a solution based synthesis of epitaxial thin films of neptunium oxide and plutonium oxide. Actinides represent a challenge to first principle calculations due to features that arise from f orbital interactions. Conventional semi-local density functional theory predicts NpO 2 and PuO 2 to be metallic, when they are well known insulators. Improvements in theory are dependent on comparison with accurate measurements of material properties, which in turn demand high-quality samples. The high melting point of actinide oxides and their inherent radioactivity makes single crystal and epitaxial film formation challenging. We report on the preparation of high quality epitaxial actinide films. The films have been characterized through a combination of X-ray diffraction and X-ray absorption fine structure (XANES and EXAFS) measurements. We report band gaps of 2.80 6 0.1 eV and 2.85 6 0.1 eV at room temperature for PuO 2 and NpO 2 , respectively, and compare our measurements with state-of-the-art calculations. V

Magnetic structure of UO2and NpO2by first-principle methods

“…The measured optical absorbance band-gap of NpO 2 epitaxial thin films is 2.85 eV. 126 In our calculations, the correct insulating nature of NpO 2 is reproduced when U = 4-6 eV for all magnetic states. In this range, the relative energy differences between the longitudinal 3k AFM, transverse 2-3k AFM, and the FM (111) states are minimal.…”

Multiple water layers on AnO2 {111}, {110}, and {100} surfaces (An = U, Pu): A computational study

“…We use 1-k co-linear magnetic ordering with a net magnetic moment of zero, allowing us to treat the total system as anti-ferromagnetic and thereby reach the correct ground state. 20,21 We neglect spin-orbit coupling, as earlier results by Rák and co-workers 22 indicate that this has only a very small effect on the surface stability. Adsorbing species are introduced on both sides of the slab to minimize dipole effects.…”

Structural, electronic, and thermodynamic properties of curium dioxide: Density functional theory calculations

“…Experimental values from Refs. [29,[68][69][70], the SIC-LSD values from Ref. [6], and the HSE values from Refs.…”