Structural, thermodynamic, electronic and elastic properties of Th1-x Ux O2 and Th1-x Pux O2 mixed oxides

Physical Chemistry Chemical Physics : PCCP
P S Ghosh, A Arya

Abstract

The structural, thermodynamic, electronic, and elastic properties of Th1-xUxO2 and Th1-xPuxO2 mixed oxides (MOX) have been calculated with Hubbard corrected density functional theory (DFT+U) to account for the strong 5f electron correlations. The ideal solid solution is approximated by special quasi-random structures and the U-ramping method is used to account for the presence of metastable states in the self-consistent field solution of the DFT+U approach. The mixing enthalpy (ΔHmix) is positive throughout the composition range of the Th1-xUxO2 MOX, consistent with a simple miscibility gap (at low temperature) phase diagram. The behavior of the Th1-xPuxO2 MOX is more complex, where ΔHmix is positive in the ThO2-rich region and negative in the PuO2-rich region. Electronic structure analysis shows that substitution of Th by U/Pu in ThO2 leads to a reduction of the average Th-O bond lengths, causing distortion in the crystal structure. The distortion in the crystal structure results in an increase in the conduction bandwidth and a reduction of the band-gap in the MOX. Good agreement of our DFT+U calculated elastic properties of ThO2, UO2 and PuO2 compounds with experiments leads to convincing prediction of these properties for Th...Continue Reading

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Jul 25, 2019·Physical Chemistry Chemical Physics : PCCP·P S Ghosh, A Arya

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Methods Mentioned

BETA
neutron capture
X-ray
AFM
inelastic neutron scattering

Software Mentioned

ATAT
Vienna Ab initio Simulation Package ( VASP )
VASP

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