Properties of helium defects in bcc and fcc metals investigated with density functional theory

Abstract

The relative stability of single He defects in bcc and fcc metals is investigated using ab initio calculations based on density functional theory. The results indicate that the tetrahedral position is energetically more favorable for a He interstitial than the octahedral site in bcc metals, but the relative stability of He defects in fcc metals varies, depending on local environments. The He formation energies in bcc Fe and fcc Ni at the tetrahedral and octahedral positions with and without spin polarization are investigated. It is of interest to find that the magnetism of host atoms does not directly affect the relative stabilities of He in interstitial sites in bcc Fe and fcc Ni.

Binding of HenV clusters to α-Fe grain boundaries

“…Calculations using this interatomic potential show that both tetrahedral and octahedral interstitials are stable, with tetrahedral He being the most stable interstitial configuration, 15 which agrees with previous ab initio calculations. 23,61 The binding properties of the He x V and He x interstitial clusters are in reasonable agreement with ab initio and previous potential results. This potential has been previously used to investigate the emission of self-interstitial atoms from small He clusters in the a-Fe matrix and to show the dissociation of a di-interstitial He cluster at temperatures >400 K. The aforementioned potential is deemed appropriate for studying the He interaction with grain boundaries in this work.…”

“…Additionally, while there is an increasing awareness of interatomic potential effects, many of the interatomic potentials used previously for some of these grain boundary studies have been improved upon with updated interatomic potential formulations 15,30,60 and/or more recent quantum mechanics results showing how magnetism affects He defects in a-Fe. 12,23,61 It has been well established that the presence of He and vacancies at the grain boundary leads to the formation/nucleation of He bubbles, both computationally and experimentally. Single helium atoms created initially are very mobile and can be easily trapped by microstructure features (e.g., grain boundaries and dislocations) forming small He clusters or He-V clusters.…”

“…There have been a number of quantum mechanics and molecular dynamics simulations that have examined how He and He clusters affect single crystal lattice properties and physical properties in a-Fe. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] For instance, density functional theory (DFT) simulations have been used to show that interstitial He atoms strongly interact with vacancies and can also be trapped by interstitial atoms (binding energy of 0.3 eV). 10 Ventelon, Wirth, and Domain 24 probed the interactions between He and self-interstitial atoms (SIAs) in a-Fe and found strong binding behavior between interstitial He and SIA clusters, which corresponded with the SIA defect strain field.…”

Атомная структура систем Zr-He, Zr-vac, Zr-vac-He: расчет из первых принципов

“…Видно, что при более высокой концентрации гелия энер-гия его растворения в междоузлиях всех рассмотренных решеток ниже соответствующих значений при концен-трации ∼ 6 at.% на 0.2−0.6 eV, за исключением октаэдри-ческого междоузлия ГЦК-решетки, где она практически не изменилась. Аналогичная зависимость энергии рас-творения от концентрации наблюдалась в работе [18] для ОЦК-переходных металлов Fe, Cr и Mo при более низких концентрациях гелия (∼ 0.8 и ∼ 1.8 at.%), при этом уменьшение энергии растворения было порядка 0.06−0.18 eV. Относительно небольшое изменение энер-гии растворения в этом случае обусловлено близостью рассмотренных концентраций.…”

“…Поэтому мы сравнили полученные нами результаты с данными тео-ретических работ, посвященных изучению энергетики систем матрица−вакансия−гелий, где в роли матрицы выступали ОЦК-(α-Fe, Cr, Mo, W, V, Nb, Ta) [6,18,30], ГЦК-(Ni, Cu, Ag, Pd) [18] и ГПУ-(Er, Sc, Y, Gd, Tb, Dy, Ho, Lu) [31][32][33] металлы. Вычисленные в этих работах энергии растворения гелия в кристалле с вакансиями имеют положительные значения, как и в нашем случае для Zr.…”