Absolute vacancy concentrations in noble metals and some of their alloys

Hehenkamp, Th.

doi:10.1016/0022-3697(94)90110-4

Cited by 83 publications

(56 citation statements)

References 39 publications

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“…This corresponds to an unphysically high concentration of vacancies. Furthermore, the results are in variance with experiments 11,12 that are indicative of a high binding energy of divacancies and a significant concentration of divacancies, especially at elevated temperatures.We study vacancy clustering and prismatic loops by performing electronic structure calculations using orbital-free density-functional theory ͑OFDFT͒. 13 Specifically, the kinetic energy functional is modeled using the Thomas-FermiWeizsacker family of functionals with =1/6.…”

supporting

confidence: 70%

supporting

confidence: 70%

“…Specifically, we found that ͗110͘ divacancies were repulsive for small cell sizes, in agreement with previous calculations, 9,10 and the same divacancies were attractive for larger cell sizes corresponding to realistic concentrations, with binding energies of 0.19 eV in agreement with experimental measurements. 11,12 This work showed that electronic structure calculations do not rule out vacancy clustering in aluminum. Therefore we examine this mechanism further in the current work.…”

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confidence: 96%

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Vacancy clustering and prismatic dislocation loop formation in aluminum

2007

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The formation of prismatic dislocation loops is an important factor leading to radiation damage of metals. However, the formation mechanism and the size of the smallest stable loop has remained unclear. In this Rapid Communication, we use electronic structure calculations with millions of atoms to address this problem in aluminum. Our results show that there is a cascade of larger and larger vacancy clusters with smaller and smaller energy. Further, the results show that a seven vacancy cluster on the ͑111͒ plane can collapse into a stable prismatic loop. This supports the long-standing hypothesis that vacancy clustering leads to a prismatic loop, and that these loops can be stable at extremely small sizes. Finally our results show that it is important to conduct calculations using realistic concentrations ͑computational cell size͒ to obtain physically meaningful results. The embrittlement of metals subjected to radiation is a long-standing problem in various applications including nuclear reactors. As the irradiation dose increases above a certain threshold, a significant population of prismatic dislocation loops ͑dislocation loops whose Burgers vector has a component normal to their plane͒ has been experimentally observed to arise in metals. [1][2][3][4][5] It is widely believed these prismatic loops form through the clustering of vacancies that are generated randomly by irradiation.6 Specifically, the vacancies diffuse and eventually cluster on specific planes. Once there is a large enough planar cluster, the atoms on the two faces collapse onto each other leaving behind a prismatic dislocation loop.However, the formation mechanism and the size of the smallest stable loop remain unclear: there is no direct experimental observation of the process, and the theoretical investigations are inconclusive. Recent molecular dynamics simulations 7 support the hypothesized mechanism for iron, but these calculations used the Finnis-Sinclair empirical atomistic potentials whose validity is uncertain in situations involving changing atomic bonds. 8 In contrast, calculations for aluminum using quantum mechanical density-functional theory 9,10 show that divacancies-a complex of two vacancies-are either energetically unfavorable if they are aligned along the ͗110͘ direction or barely favorable with negligible binding energy if aligned along ͗100͘. If two vacancies can barely bind, it seems doubtful that they can be stable and grow to form clusters that can turn into prismatic loops. While these density-functional theory ͑DFT͒ methods are far more accurate, the computational effort is extremely large and consequently these calculations were limited to less than 100 atoms. This corresponds to an unphysically high concentration of vacancies. Furthermore, the results are in variance with experiments 11,12 that are indicative of a high binding energy of divacancies and a significant concentration of divacancies, especially at elevated temperatures.We study vacancy clustering and prismatic loops by performing electronic structure c...

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supporting

confidence: 70%

supporting

confidence: 70%

mentioning

confidence: 96%

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Vacancy clustering and prismatic dislocation loop formation in aluminum

2007

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“…Al calculations, experiments, and other many-body potentials that include tight-binding (TB) model, simple analytical (SAEAM) and modified version (MEAM) of embedded-atom method [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. The fits to equilibrium lattice parameter, the cohesive energy, the vacancy formation energy, and elastic constants are quite good for both Al and Cu.…”

Section: Parametermentioning

confidence: 99%

Monte Carlo simulations of strain-driven elemental depletion or enrichment in Cu95Al5 and Cu90Al10 alloys

Deng

Tang

et al. 2015

Computational Materials Science

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“…[20] a is the lattice constant. C v is the equilibrium vacancy concentration and is described by an equation of the form [21] :…”

Section: First-principles Calculationsmentioning

confidence: 99%

Self-Diffusion Coefficient of fcc Mg: First-Principles Calculations and Semi-Empirical Predictions

Zhao

Kong

Wang

et al. 2011

J. Phase Equilib. Diffus.

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First-principles calculations and semi-empirical equations are employed to determine the selfdiffusion mobility of fcc Mg. All factors entering the vacancy-mediated self-diffusion coefficient, which include the equilibrium lattice parameter, the enthalpy of vacancy formation and atom migration, and the vibrational entropy of vacancy formation as well as the effective frequency, are evaluated with the local density approximation (LDA) and generalized gradient approximation (GGA) in first-principles calculations. These computed quantities are then utilized to calculate the self-diffusion coefficient of fcc Mg. For comparison, four widely used semiempirical equations are also used to estimate the self-diffusion coefficient of fcc Mg. The comparisons show that first-principles calculations and semi-empirical equations yield values close to the activation energy Q for self-diffusion of fcc Mg from the LDA calculation, but the diffusion prefactor D 0 predicted from the four semi-empirical equations are all about one order of magnitude larger than those from the first-principles calculations. Based on the comparison for the self-diffusion coefficients of fcc Al computed with the first-principles method and semiempirical approaches, it is concluded that the self-diffusion coefficient of fcc Mg calculated with the LDA method is more accurate than the estimation from semi-empirical approaches.

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Absolute vacancy concentrations in noble metals and some of their alloys

Cited by 83 publications

References 39 publications

Vacancy clustering and prismatic dislocation loop formation in aluminum

Vacancy clustering and prismatic dislocation loop formation in aluminum

Monte Carlo simulations of strain-driven elemental depletion or enrichment in Cu95Al5 and Cu90Al10 alloys

Self-Diffusion Coefficient of fcc Mg: First-Principles Calculations and Semi-Empirical Predictions

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