A first principles study of the electronic structure, elastic and thermal properties of UB2

Jossou, Ericmoore; Malakkal, Linu; Szpunar, Barbara; Oladimeji, Dotun; Szpunar, Jerzy A.

doi:10.1016/j.jnucmat.2017.04.006

Cited by 26 publications

(13 citation statements)

References 36 publications

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“…The displacements are also restricted to in-plane neighbours only. This is consistent with the anisotropic elastic constant matrix (Table 1), dielectric tensor, and metallic-covalent nature of the material, which was reported to have covalent bond in plane and metallic bonds out of plane [9,13,38] (also evident in the charge density distribution of Figure 5). Conveniently, this enables the study of reasonably large defect clusters (e.g.…”

Section: Defect Reactionsupporting

confidence: 88%

“…Past work simulating UB 2 using DFT methods [9,14] has used an on-site Coulomb repulsion term '+U', also known as the Hubbard parameter. The magnitude of this parameter, and whether it is required at all, is entirely dependent on the material chemistry and crystal structure, and it is not transferable from one compound to a chemically similar but structurally different compound (or viceversa structurally similar but chemically different).…”

Section: Methodsmentioning

confidence: 99%

“…Uranium diboride has a high melting point of 2430 • C [8] and high uranium density (11.68 g cm −3 ), greater than that of UO 2 (9.67 g cm −3 ). Theoretical studies have also reported that UB 2 exhibits an extraordinary thermal conductivity of 52 Wm −1 K −1 in its un-irradiated state [9]. Experimental efforts have yielded a thermal conductivity of approximately a factor of two lower [10], which is still a remarkably high thermal conductivity.…”

Section: Uranium Diboridementioning

confidence: 99%

“…The single-crystal elastic constants, c ij , were calculated through perturbation theory and from these the polycrystalline bulk and shear moduli were obtained using a Hill average of the Reuss and Voight method [33]. These are presented in Table 1, and compared with previous DFT values of Jossou et al [9] and experimental bulk modulus of Dancausse et al [32]. Despite the similarities in methodology between the two DFT studies 1 , there are remarkable differences for some of the stiffness constants, exemplified clearly by the varied shear constant values.…”

Section: Bulk Propertiesmentioning

confidence: 99%

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Defect evolution in burnable absorber candidate material: Uranium diboride, UB2

Burr¹,

Kardoulaki²,

Holmes³

et al. 2019

Journal of Nuclear Materials

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The stability, diffusivity and clustering behaviour of defects in uranium diboride (UB 2) was investigated in light of the potential application as a burnable absorber in nuclear fuel. UB 2 was found to accommodate limited deviations from stoichiometry, which should be a consideration when manufacturing and operating the material. Self-diffusivity of both U and B was found to be sluggish (10 −14 cm 2 /s for B and 10 −19 cm 2 /s for U at 2000 K) and highly anisotropic, with migration along the basal planes being orders of magnitude faster than c-axis migration. The anisotropy of defect migration (both interstitials and vacancies) is predicted to hinder recombination of defects produced by collision cascades, thus limiting the radiation tolerance of the material. Boron and uranium vacancies exhibit a drive to cluster. Boron vacancies in particular, which are mobile on basal planes, are predicted to cluster into strongly bound di-vacancy, which in turn are less mobile. These are then predicted to grow into larger two-dimensional vacancy clusters on the B plane, leading to anisotropic swelling. We provide an analytical expression to predict the stability of these clusters based on purely geometrical considerations. Finally, the accommodation of Li, He and Xe onto vacancy clusters was considered. Li appears to stabilise the structure upon U depletion, while the retention of He and Xe appears to rise with increasing B depletion, through the formation of vacancy clusters.

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Section: Defect Reactionsupporting

confidence: 88%

Section: Methodsmentioning

confidence: 99%

Section: Uranium Diboridementioning

confidence: 99%

Section: Bulk Propertiesmentioning

confidence: 99%

See 2 more Smart Citations

Defect evolution in burnable absorber candidate material: Uranium diboride, UB2

Burr¹,

Kardoulaki²,

Holmes³

et al. 2019

Journal of Nuclear Materials

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show abstract

“…Traditionally metal oxides were used as fuel since they have a high melting point [1]. Nitrides and Borides (with the appropriate isotopic composition that excludes strong neutron absorber 10 B) are also attracting attention due to their large thermal conductivity from the electronic contribution that increases with increasing temperature [2,3]. In this work, we evaluate the thermal conductivity of ceramic composites where the heat carriers are primarily phonons.…”

Section: Introductionmentioning

confidence: 99%

Accident tolerant composite nuclear fuels

et al. 2017

Self Cite

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Abstract. Investigated accident tolerant nuclear fuels are fuels with enhanced thermal conductivity, which can withstand the loss of coolant for a longer time by allowing faster dissipation of heat, thus lowering the centerline temperature and preventing the melting of the fuel. Traditional nuclear fuels have a very low thermal conductivity and can be significantly enhanced if transformed into a composite with a very high thermal conductivity components. In this study, we analyze the thermal properties of various composites of mixed oxides and thoria fuels to improve thermal conductivity for the next generation safer nuclear reactors.

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Influence of Local Lattice Distortion on Elastic Properties of Hexagonal Close‐Packed TiZrHf and TiZrHfSc Refractory Alloys

Meng

Duan

Chen

et al. 2021

Physica Status Solidi (b)

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The unique mechanical properties and local lattice distortion (LLD) for hexagonal close‐packed (HCP) multiple principal element alloys (MPEAs) are very rarely studied so far. Employing density functional theory calculation based on special quasirandom structure, this work studies the influences of LLD on elastic properties for both novel hexagonal TiZrHf(Sc) MPEAs. Compared to the pristine structures, the lattice stability of distorted random structures is improved evidently. Moreover, LLD obviously lessens the shear elastic properties, which may be an ubiquitous phenomenon irrespective of the lattice types of MPEAs. These results also uncover the apparent improvement in malleable behavior and shear anisotropy for HCP MPEAs. So, the influence of LLD on elastic properties for HCP MPEAs is profound. The degree of LLD is further studied via the standard deviation of near‐neighbor (NN) and next NN bond length distributions as an effective indicator of LLD. More significant distortion uncovered in TiZrHf alloy corresponds consistently to the stronger effects of LLD in TiZrHf alloy. Bader's charge and charge density distribution also demonstrate the underlying impact on LLD for both HCP MPEAs, so electronic nature is a significant factor for LLD. The present study provides guideline for designing mechanical properties of TiZrHf‐based HCP MPEAs engineering materials.

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A first principles study of the electronic structure, elastic and thermal properties of UB2

Cited by 26 publications

References 36 publications

Defect evolution in burnable absorber candidate material: Uranium diboride, UB2

Defect evolution in burnable absorber candidate material: Uranium diboride, UB2

Accident tolerant composite nuclear fuels

Influence of Local Lattice Distortion on Elastic Properties of Hexagonal Close‐Packed TiZrHf and TiZrHfSc Refractory Alloys

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