Stability and kinetics of helium interstitials in boron carbide from first principles

Schneider, Annemarie; Roma, Guido; Crocombette, Jean-Paul; Motte, Vianney; Gosset, Dominique

doi:10.1016/j.jnucmat.2017.09.020

Cited by 15 publications

(32 citation statements)

References 25 publications

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“…In a previous theoretical work we showed how helium interstitial 2D diffusion could bias the shape of helium bubbles [25]. A subsequent theoretical study [26] has confirmed our results for He and investigated the mobility of lithium, the other product of the nuclear reaction triggered by 10 B neutron absorption.…”

Section: Introductionsupporting

confidence: 77%

“…Our charged vacancies calculations confirm that chain vacancies are more favorable than icosahedral vacancies [25,26], especially the boron chain center vacancy which is the most stable vacancy in the structure by far.…”

Section: Stability and Mobility Of An Isolated Vacancysupporting

confidence: 54%

“…Total energies were computed with the open-source code Quantum Espresso [35] using a GGA-based vdW-DF functional [36] which combines an optimized Becke86 exchange component with non-local van der Waals correlation part, as used in a previous work on He in boron carbide [25]. Defect calculations were carried out in a 2×2×2 supercell to approach the dilute limit of the defect.…”

Section: Computational Detailsmentioning

confidence: 99%

“…The introduction of vacancies in the model allows us to consider diffusion mechanisms other than the direct interstitial mechanism previously studied by Schneider et al [25]. Indeed with the presence of intrinsic vacancies and interstitial impurities comes the possibility of substitutional impurity formation.…”

Section: Helium Impurities and Vacanciesmentioning

confidence: 99%

“…To evaluate the effect of vacancies on the direct interstitial mechanism, the interactions between interstitial helium impurities and vacancies were studied. To remind the work of Schneider et al [25], the two dominant types of helium interstitials sites are called "Type 2" and "Type 3" (or P2 and P3, see Fig. 7).…”

Section: Helium Impurities and Vacanciesmentioning

confidence: 99%

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The influence of irradiation induced vacancies on the mobility of helium in boron carbide

Gillet

Roma

Crocombette

et al. 2018

Journal of Nuclear Materials

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Boron carbide, used as a neutron absorber, undergoes nuclear reactions producing relevant quantities of He. The understanding of He kinetics at the atomic scale in the material is still in its infancy, in spite of decades of experimental work devoted to the characterization of He containing, irradiated, boron carbide samples. The interplay of He itself with intrinsic defects created by irradiation on kinetics is still almost completely unknown. In this paper we present an exhaustive study of vacancies and substitutional helium impurities in boron carbide using Density Functional Theory. Analyzing the stability and mobility of these defects allows us to consider diffusion mechanisms other than the known interstitial mechanisms. We find that vacancies trap He interstitials, raising the activation energy of 2D diffusion to approximately 2 eV. The trapping mechanism is different according to the charge state of the vacancy : in p-type conditions, when vacancies are neutral or positive, He diffuses via a dissociative mechanisms and is trapped in a substitutional position; in n-type conditions, negative vacancies trap He atoms traveling in an adjacent {111} plane by a charge transfer driven distorsion. No favorable vacancy assisted diffusion mechanism was identified for substitutional He atoms, except the dissociative one previously mentioned. Other possible vacancy diffusion mechanisms, which we also analyzed, are hindered by the high activation energy of vacancy self-diffusion.

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Section: Introductionsupporting

confidence: 77%

Section: Stability and Mobility Of An Isolated Vacancysupporting

confidence: 54%