Institute Tecnologia J Sabato

San Martín, Argentina

Institute Tecnologia J Sabato

San Martín, Argentina
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Gargano P.H.,Comision Nacional de la Energia Atomica | Gargano P.H.,Institute Tecnologia J Sabato | Kniznik L.,Comision Nacional de la Energia Atomica | Kniznik L.,Institute Tecnologia J Sabato | And 7 more authors.
Journal of Nuclear Materials | Year: 2016

The point defect structure of intermetallic compound oI20 UAl4 is investigated using a combination of the statistical mechanical Wagner-Schottky model and first-principles calculations within a projector augmented wave pseudopotential method in conjunction with the generalized gradient approximation. The formation energies of eight point defects were calculated taking into account the four sublattices. The point defect concentrations are calculated as function of temperature and deviation from stoichiometry. Our results show that the aluminum antisite is the constitutional point defect on the Al-rich side. At this off-stoichiometric side the dominant thermal defect is an interbranch defect where four constitutional antisite aluminum atoms are replaced by five uranium vacancies. The point defect effective formation energies are obtained and these results allow us to identify the antistructure bridge mechanism as the most probable for the diffusion for Al atoms in the Al-rich UAl4 intermetallic compound. © 2016 Elsevier B.V. All rights reserved.


Kniznik L.,Comision Nacional de la Energia Atomica | Alonso P.R.,Comision Nacional de la Energia Atomica | Alonso P.R.,Institute Tecnologia J Sabato | Gargano P.H.,Comision Nacional de la Energia Atomica | And 4 more authors.
Journal of Nuclear Materials | Year: 2011

In this work the growth of the UAl 4 phase in an UAl 3/Al diffusion couple is treated as a planar moving boundary problem due to diffusion of Al and U atoms in the direction perpendicular to the interface surface. The diffusion problem was carried out by the DICTRA simulation package which combines data evaluated by Thermo-Calc with a mobility database. A thermodynamic database of the U-Al system, suitable for the Thermo-Calc code, was composed using data from literature. The mobility database was assessed from reported experimental growth of the UAl 4 phase at different temperatures. The Al tracer diffusion coefficient in the UAl 4 phase, DAl(UAl 4)(m 2/s)=2.7×10 -1exp(-209500(J/mol)/RT), is obtained under the assumption that uranium mobility is negligible. © 2010 Elsevier B.V. All rights reserved.


Kniznik L.,Comision Nacional de la Energia Atomica | Kniznik L.,Institute Tecnologia J Sabato | Alonso P.R.,Comision Nacional de la Energia Atomica | Alonso P.R.,Institute Tecnologia J Sabato | And 5 more authors.
Journal of Nuclear Materials | Year: 2015

UAl4 ideal and defect structures were studied within the framework of the Density Functional Theory. The structural and magnetic ordering of UAl4 in paramagnetic, ferromagnetic, and antiferromagnetic states have been investigated, within the collinear and non-collinear spin approximation, using the GGA model, as embedded in the program package VASP. An antiferromagnetic (01¯1) layer structure with spins aligned to the [010] direction was found to be energetically preferred. The analysis of density of states and bonding charge density point out that the bonding mechanism consists primarily of band mixing between the U 5f and Al 3p states. Supercells were built from UAl4 unit cells with the established magnetic structure. For those supercells we calculated the energy of formation of vacancies and antisite defects taking into account the existence of three distinct aluminum sites. Point defect formation energies, local lattice relaxations, as well as the defect induced magnetic ordering and electronic density redistribution, are discussed. It is shown that antiferromagnetism is locally broken. Al antisites and U antisites in Al 4e Wyckoff positions are the constitutional point defects in Al-rich and U-rich oI20 UAl4, respectively. In this way we have presented here the first set of data which makes it possible to discuss and quantify the point defects concentrations in the experimental composition range for existence of this uranium aluminide. © 2015 Elsevier B.V. All rights reserved.

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