Computer simulation of SIA migration in bcc and hcp metals

Pasianot, R.C.; Monti, A. M.; Simonelli, G.; Savino, E. J.

doi:10.1016/s0022-3115(99)00182-8

Cited by 44 publications

(25 citation statements)

References 19 publications

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“…Their study concluded that diffusion on strained Cu is mediated by the formation and motion of a surface crowdion. The high mobility of crowdions has also been reported for several metals [37][38][39] . In the present investigation, we explore the dominant diffusion mechanisms on W(001) and W(110) surfaces with more precise first-principles calculations in order to reveal the electronic origin of the effects of an applied strain field on adatom motion.…”

Section: Model and Methodologymentioning

confidence: 56%

Biaxial strain effects on adatom surface diffusion on tungsten from first principles

Chen

Ghoniem

2013

Phys. Rev. B

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Using first-principles electronic structure calculations, the energy barriers for diffusion mechanisms of adatoms on the tungsten (W) (001) and (110) surfaces under externally-applied biaxial strain fields are determined. Adatoms move either by hopping on the surface or by an exchange process with a surface atom, which is found to be completed in one step (direct exchange), or via the formation of a surface crowdion (crowdion-mediated exchange). As a result of the compact atomic stacking, hopping is found to be the major diffusion mechanism on the W(110) surface, irrespective of the surface strain state. On the other hand, the main diffusion mechanism on the less compact W(001) surface is found to be a competition between direct exchange and crowdion-mediated exchange, depending on the magnitude of the surface biaxial strain. Results of the model reveal that, if surface crowdions form, they will be highly mobile and migrate anisotropically. A microscopic explanation is presented by analyzing the charge density associated with surface crowdions. A "mechanism diagram"for atomic surface diffusion on the W(001) indicates that the diffusion direction and its rate can both be modulated by an applied biaxial strain. Migration volumes for the three mechanisms are calculated, and the significance of the results to the understanding of surface evolution under plasma or other energetic ion bombardment is highlighted.

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Section: Model and Methodologymentioning

confidence: 56%

Biaxial strain effects on adatom surface diffusion on tungsten from first principles

Chen

Ghoniem

2013

Phys. Rev. B

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“…The stable interstitial is the 111 -split configuration in V, but the 110 -split configuration in Fe and Mo. In the Fe and Mo cases, the split interstitial sits in the 110 -orientation until it is thermally activated into one of the 111 -directions where it can migrate easily before returning to a 110 -orientation [15]. There are no relaxation events of this type in interstitial migration in V. Here, the stable 111 -split interstitial migrates long distances and only requires significant thermal activation to reorient or rotate.…”

Section: (B)mentioning

confidence: 99%

Strongly non-Arrhenius self-interstitial diffusion in vanadium

et al. 2004

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We study diffusion of self-interstitial atoms (SIAs) in vanadium via molecular dynamics simulations. The 111 -split interstitials are observed to diffuse one-dimensionally at low temperature, but rotate into other 111 directions as the temperature is increased. The SIA diffusion is highly non-Arrhenius. At T < 600 K, this behavior arises from temperature-dependent correlations. At T > 600 K, the Arrhenius expression for thermally activated diffusion breaks down when the migration barriers become small compared to the thermal energy. This leads to Arrhenius diffusion kinetics at low T and diffusivity proportional to temperature at high T . The creation and migration of self-interstitial atoms (SIAs) are critical for microstructural evolution of materials in a variety of situations, such as in the high energy radiation environment of nuclear reactors [1] and in ion implantation [2]. Although SIA formation energies are much larger than typical thermal energies, they form in abundance during collision cascades induced by impinging energetic particles. SIAs in metals are typically very mobile (i.e., their migration barriers are relatively small) and hence play an important role in controlling the rates of many microstructural processes in such applications, in particular the phenomenon of void swelling.Since SIA properties and mobilities are very difficult to determine experimentally, one often employs computer simulations [3,4,5,6]. For example, simulations of body centered cubic (bcc) iron (and several other bcc metals), have shown that SIAs preferentially lie along 110 orientations but rotate into 111 -directions, where they can migrate easily using the crowdion configuration as transition state. Other simulations have suggested that SIA migration in vanadium is very similar to that in Fe [7,8,9,10]. However, these empirical interatomic potential-based simulations are not consistent with recent first principles calculations that clearly show that the lowest energy SIA configuration in V is a 111 -split interstitial, rather than the 110 -split configuration found in Fe [11]. Interestingly, the first principles calculations also revealed that the 111 -oriented SIA migration energy is extraordinarily small (≤ 0.01eV), which explains the experimental observation of diffusion down to 4 K [12]. SIA migration in Fe and V must therefore differ in their microscopic mechanisms.We perform a series of molecular dynamics (MD) sim- † current address: Department of Physics, Ewha Womans University, Seoul 120-750, Korea.ulation of SIA migration in V using an improved interatomic potential for V [13] (refit to experimental and first principles data [11] to reproduce the stable interstitial configuration) to address this discrepancy. In particular, we examine SIA diffusion as a function of temperature to determine the SIA migration mechanisms. We find that while SIA migration in V is similar to that in bcc Fe in many respects, its temperature dependence is highly unusual, exhibiting strongly non-Arrhenius behavior and correlation ef...

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“…Although the detailed mechanism is not given here, the present retracing phenomenon is associated with the results of colliding crowdions; the retracement is suggested to be caused essentially by an interaction between a moving crowdion and lattice phonons, which casually give rise to a locally crowdion-like dense arrangement of atoms having vibrational energies (estimated to be h $ 10 À2 eV for $ 8 THz, the highest phonon frequency of iron) comparable to the kinetic energy of a migrating crowdion (E k > 6:0 Â 10 À3 eV). A careful inspection may point out that the retracing phenomenon of an SIA has been already visualized in figures presented in literatures, 1,2) but unfortunately it is a little hard to recognize it distinctly.…”

mentioning

confidence: 93%

“…Recently, molecular-dynamics (MD) simulations have revealed unusual behaviors of irradiation-induced self-interstitial atoms (SIAs); strong migrational anisotropy along a specific crystallographic direction 1,2) as well as ultra-high mobility when they are clustered. 3,4) An SIA in bcc-iron has two allotropic configurations; one is stable being composed of two dumbbell atoms splitting over a lattice point with their bonding axis laid on a h110i direction, and the other is metastable being at an excited state with its bonding axis rotated from the h110i direction to a h111i direction according to the Fermi-Dirac distribution function.…”

Section: Introductionmentioning

confidence: 99%

Solitonic Migration and Collisions of Self-Interstitial Defects in BCC Iron

Kusunoki

2006

Mater. Trans.

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Self-interstitial atoms in bcc iron display unusual migration behaviors; strong anisotropy toward a h111i direction with occasional rotation to an equivalent direction as well as retracing the same way as it has come, and also ultra-high mobility when they are clustered. These singularities cannot be explained by simple interstitial or interstitialcy diffusion mechanisms. However, some of them will be well accounted if the SIA could behave as a soliton, which makes three-dimensional movements in appearance, but essentially a serial combination of onedimensional migration. Indeed, a crowdion, one of isomeric configurations of the self-interstitial atom, has an atomic arrangement very similar to the one-dimensional dislocation core structure, whose migration kinetics has been well modelled by a one-dimensional soliton equation. Here we report a decisive observation that both a single and colliding two crowdions really behave as solitons in iron crystals using molecular dynamics simulations. In addition, we ascertain that the present results are attributed to the intrinsic nature of the crowdion where an overall potential felt by atoms therein is very shallow and periodical along the migration direction.

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Computer simulation of SIA migration in bcc and hcp metals

Cited by 44 publications

References 19 publications

Biaxial strain effects on adatom surface diffusion on tungsten from first principles

Biaxial strain effects on adatom surface diffusion on tungsten from first principles

Strongly non-Arrhenius self-interstitial diffusion in vanadium

Solitonic Migration and Collisions of Self-Interstitial Defects in BCC Iron

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