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

Author:
Ericmoore Jossou  Linu Malakkal  Barbara Szpunar  Dotun Oladimeji  Jerzy A. Szpunar  


Journal:
Journal of Nuclear Materials


Issue Date:
2017


Abstract(summary):

Abstract Uranium diboride (UB 2 ) has been widely deployed for refractory use and is a proposed material for Accident Tolerant Fuel (ATF) due to its high thermal conductivity. However, the applicability of UB 2 towards high temperature usage in a nuclear reactor requires the need to investigate the thermomechanical properties, and recent studies have failed in highlighting applicable properties. In this work, we present an in-depth theoretical outlook of the structural and thermophysical properties of UB 2 , including but not limited to elastic, electronic and thermal transport properties. These calculations were performed within the framework of Density Functional Theory (DFT) + U approach, using Quantum ESPRESSO (QE) code considering the addition of Coulomb correlations on the uranium atom. The phonon spectra and elastic constant analysis show the dynamic and mechanical stability of UB 2 structure respectively. The electronic structure of UB 2 was investigated using full potential linear augmented plane waves plus local orbitals method (FP-LAPW+lo) as implemented in WIEN2k code. The absence of a band gap in the total and partial density of states confirms the metallic nature while the valence electron density plot reveals the presence of covalent bond between adjacent B-B atoms. We predicted the lattice thermal conductivity ( k L ) by solving Boltzmann Transport Equation (BTE) using ShengBTE. The second order harmonic and third-order anharmonic interatomic force constants required as input to ShengBTE was calculated using the Density-functional perturbation theory (DFPT). However, we predicted the electronic thermal conductivity ( kel ) using Wiedemann-Franz law as implemented in Boltztrap code. We also show that the sound velocity along ‘a’ and ‘c’ axes exhibit high anisotropy, which accounts for the anisotropic thermal conductivity of UB 2 . Graphical abstract Image 1 Highlights • Prediction of electronic structure and thermophysical properties of UB 2 using DFT calculations. • Computation of the total thermal conductivity using a combination of Boltzmann transport equation and Wiedemann–Franz law. • We showed directional dependence of lattice assisted thermal conductivity of UB 2 .


Page:
41-41


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