<i>Ab initio</i>study of uranyl peroxides: Electronic factors behind the phase stability

Ostanin, S.; Zeller, Ph.

doi:10.1103/physrevb.75.073101

Cited by 31 publications

(46 citation statements)

References 19 publications

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“…[28][29][30] Although theoretical approaches that go beyond standard DFT are needed to account for the strong on-site Coulomb repulsion between U 5f electrons in bulk UO 2 , previous studies on studtite and uranyl-organic coordination polymers show that standard DFT is appropriate to describe those systems. 24,30 The interaction between valence electrons and ionic cores was described by the projector augmented wave (PAW) method. 31,32 The U(6s,6p,6d,5f,7s) and O(2s,2p) electrons were treated explicitly as valence electrons in the Kohn-Sham (KS) equations and the remaining core electrons together with the nuclei were represented by PAW pseudopotentials.…”

Section: Methodsmentioning

confidence: 99%

Structures of uranyl peroxide hydrates: a first-principles study of studtite and metastudtite

et al. 2012

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2 ], have been investigated using density functional theory. The structure of metastudtite crystallizing in the orthorhombic space group Pnma (Z = 4) is reported for the first time at the atomic level and the computed lattice parameters, a = 8.45, b = 8.72, c = 6.75 Å, demonstrate that the unit cell of metastudtite is larger than previously reported dimensions (Z = 2) derived from experimental X-ray powder diffraction data.

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Section: Methodsmentioning

confidence: 99%

Structures of uranyl peroxide hydrates: a first-principles study of studtite and metastudtite

et al. 2012

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“…In fact, for a numerous set of materials in which uranium exists with VI oxidation state, the standard DFT description provides a reliable description of their structures and properties. [113][114][115][116][117][118][119][120][121][122][123][124][125][139][140][141][142][143][144][155][156][157][158][159][160][161][162] 2.2.2. Elastic tensor and equation of state.…”

Section: Introductionmentioning

confidence: 99%

Structural, mechanical, spectroscopic and thermodynamic characterization of the copper-uranyl tetrahydroxide mineral vandenbrandeite

et al. 2019

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“…The water molecules are located on two different positions between these chains. Although there are different, yet very similar, models for metastudtite, thus far no structure has been determined (7,8). It is highly probable that metastudtite, like studtite, consists of chains of edge-sharing UO 8 polyhedra with the water molecules located between the chains.…”

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Energetics of metastudtite and implications for nuclear waste alteration

Guo

Ushakov

Labs

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Metastudtite, (UO 2 )O 2 (H 2 O) 2 , is one of two known natural peroxide minerals, but little is established about its thermodynamic stability. In this work, its standard enthalpy of formation, −1,779.6 ± 1.9 kJ/mol, was obtained by high temperature oxide melt drop solution calorimetry. Decomposition of synthetic metastudtite was characterized by thermogravimetry and differential scanning calorimetry (DSC) with ex situ X-ray diffraction analysis. Four decomposition steps were observed in oxygen atmosphere: water loss around 220°C associated with an endothermic heat effect accompanied by amorphization; another water loss from 400°C to 530°C; oxygen loss from amorphous UO 3 to crystallize orthorhombic α-UO 2.9 ; and reduction to crystalline U 3 O 8 . This detailed characterization allowed calculation of formation enthalpy from heat effects on decomposition measured by DSC and by transposed temperature drop calorimetry, and both these values agree with that from drop solution calorimetry. The data explain the irreversible transformation from studtite to metastudtite, the conditions under which metastudtite may form, and its significant role in the oxidation, corrosion, and dissolution of nuclear fuel in contact with water. Metastudtite is the main natural peroxide mineral (1) due to the irreversible dehydration of studtite (2). Both these phases may be found in spent nuclear fuel exposed to water (3-5). Burns et al. (6), by single crystal diffraction of a natural sample, determined the crystal structure of studtite to be monoclinic with space group C2/c. The structure consists of edge-sharing UO 8 -polyhedra chains. The water molecules are located on two different positions between these chains. Although there are different, yet very similar, models for metastudtite, thus far no structure has been determined (7,8). It is highly probable that metastudtite, like studtite, consists of chains of edge-sharing UO 8 polyhedra with the water molecules located between the chains. To better depict the bonding situation and the different oxygen atoms, it is proposed to write the sum formulas as (UO 2 )(O 2 )(H 2 O) 2 ·2H 2 O for studtite and (UO 2 )(O 2 )(H 2 O) 2 for metastudtite [in analogy to Burns et al. (6)].Studtite and other polyoxouranylates have a potentially important role as alteration phases in geological repositories for nuclear waste, specifically regarding the interactions of nuclear waste with the aqueous environment (9, 10). They have also been proposed as corrosion products in sea water after the FukushimaDaiichi nuclear plant accident (10-12).In a nuclear waste repository, the high alpha dosage will be the dominant factor after the first thousand years of storage (13). In combination with groundwater, the alpha radiation will lead to formation of H 2 O 2 (3, 4, 9, 14). These very localized oxidative conditions could trigger the genesis of studtite or metastudtite even if the overall conditions are reducing (14). The formation of metastudtite on UO 2 samples as a direct effect of alpha radiolysis of water w...

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Ab initiostudy of uranyl peroxides: Electronic factors behind the phase stability

Cited by 31 publications

References 19 publications

Structures of uranyl peroxide hydrates: a first-principles study of studtite and metastudtite

Structures of uranyl peroxide hydrates: a first-principles study of studtite and metastudtite

Structural, mechanical, spectroscopic and thermodynamic characterization of the copper-uranyl tetrahydroxide mineral vandenbrandeite

Energetics of metastudtite and implications for nuclear waste alteration

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