A combined effect of vacancies and segregated impurities at grain boundaries in nickel

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00216224%3A14310%2F19%3A00113688" target="_blank" >RIV/00216224:14310/19:00113688 - isvavai.cz</a>

Výsledek na webu

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DOI - Digital Object Identifier

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Jazyk výsledku

angličtina

Název v původním jazyce

A combined effect of vacancies and segregated impurities at grain boundaries in nickel

Popis výsledku v původním jazyce

This work presents a detailed ab initio study of interactions between grain boundary (GB), impurities X (X = Al, Si) and vacancies (Va) in fcc ferromagnetic nickel. As a basis of our calculations, supercells containing 60 or 120 atoms, complemented by the tilt sigma 5(210) GB, were used. The calculations were performed within the density functional theory using the VASP code with projector-augmented plane wave (PAW) potentials. Two possible approaches to equilibration of structure (full relaxation and relaxation with fixed lattice parameters in the GB plane) are presented and discussed. In our study the following GB configurations were investigated (superscripts (i) or (s) mean an impurity atom in an interstitial or substitutional position, respectively): GB Ni120Si2(i), GB Ni60, GB Ni120, GB Ni118Al2(s) and GB Ni118Si2(s). By addition of a vacancy to the above-mentioned structures, it was found that vacancies at this GB may lose their open volume in the most stable configurations, which results in a change of the GB structure. The energy of formation of the structures with GB, vacancy and impurity is positive. The binding energy of a vacancy to a combined defect GB+X is negative for all structures. The inclusion of an X+Va pair into the structure containing GBs is energetically favourable, if calculated with respect to two reference states: “structure with GB, but without any vacancy and impurity” and “impurity in the standard element state”. As fcc Ni is a ferromagnetic metal, the change of the distribution of magnetic moments on particular atoms caused by impurities, vacancies and GBs was also studied. It was found that Al and Si impurities gain a magnetic moment with antiparallel orientation and the magnetic moment of neighbouring nickel atoms decreases. On the other hand, the presence of a vacancy causes an increase of magnetic moments of neighbouring Ni atoms. However, the “magnetic moment decreasing” effect of an impurity with a negative induced magnetic moment is usually larger than the “magnetic moment increasing” effect of a vacancy. It was concluded that the distance from the impurity has the dominating influence on the magnetism of Ni atoms in comparison to the distance from the vacancy or GB. As there is very little experimental information on interaction between impurities, vacancies and GBs in fcc nickel, most of the present results are theoretical predictions which may motivate future experimental work.

Název v anglickém jazyce

A combined effect of vacancies and segregated impurities at grain boundaries in nickel

Popis výsledku anglicky

This work presents a detailed ab initio study of interactions between grain boundary (GB), impurities X (X = Al, Si) and vacancies (Va) in fcc ferromagnetic nickel. As a basis of our calculations, supercells containing 60 or 120 atoms, complemented by the tilt sigma 5(210) GB, were used. The calculations were performed within the density functional theory using the VASP code with projector-augmented plane wave (PAW) potentials. Two possible approaches to equilibration of structure (full relaxation and relaxation with fixed lattice parameters in the GB plane) are presented and discussed. In our study the following GB configurations were investigated (superscripts (i) or (s) mean an impurity atom in an interstitial or substitutional position, respectively): GB Ni120Si2(i), GB Ni60, GB Ni120, GB Ni118Al2(s) and GB Ni118Si2(s). By addition of a vacancy to the above-mentioned structures, it was found that vacancies at this GB may lose their open volume in the most stable configurations, which results in a change of the GB structure. The energy of formation of the structures with GB, vacancy and impurity is positive. The binding energy of a vacancy to a combined defect GB+X is negative for all structures. The inclusion of an X+Va pair into the structure containing GBs is energetically favourable, if calculated with respect to two reference states: “structure with GB, but without any vacancy and impurity” and “impurity in the standard element state”. As fcc Ni is a ferromagnetic metal, the change of the distribution of magnetic moments on particular atoms caused by impurities, vacancies and GBs was also studied. It was found that Al and Si impurities gain a magnetic moment with antiparallel orientation and the magnetic moment of neighbouring nickel atoms decreases. On the other hand, the presence of a vacancy causes an increase of magnetic moments of neighbouring Ni atoms. However, the “magnetic moment decreasing” effect of an impurity with a negative induced magnetic moment is usually larger than the “magnetic moment increasing” effect of a vacancy. It was concluded that the distance from the impurity has the dominating influence on the magnetism of Ni atoms in comparison to the distance from the vacancy or GB. As there is very little experimental information on interaction between impurities, vacancies and GBs in fcc nickel, most of the present results are theoretical predictions which may motivate future experimental work.

Druh

O - Ostatní výsledky

CEP obor

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OECD FORD obor

10403 - Physical chemistry

Projekt

<a href="/cs/project/LQ1601" target="_blank" >LQ1601: CEITEC 2020</a><br>

Návaznosti

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)<br>S - Specificky vyzkum na vysokych skolach

Rok uplatnění

2019

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů