| During the nuclear reaction,core materials under high-energy radiation will generate vacancies and interstitials,which will evolve into defect clusters,dislocations and grain boundaries.Finally,it would result in swelling,high temperature intergranular embrittlement,surface roughening and blistering that decrease the mechanical properties of materials.Hence,it's necessary to research and develop new irradiation resistant materials for advanced nuclear energy systems.Due to the exceptional properties of graphene,some graphene-based materials have exceedingly good properties and promising application prospect.Research indicates that graphene in metal-graphene layered composites can block dislocation propagation and copper-graphene layered composites may have excellent ability to resist radiation damage.In order to thoroughly understanding the radiation tolerance of metal-graphene layered composites,further investigation of point defect behaviors near the interface of the metal/graphene/metal is necessary.In this work,the formation and migration behavior of point defects near the interface of the metal/graphene/metal were investigated by VASP code based on the first-principles method.The main contents and results are as follows:1.The point defect properties of copper/graphene/copper(Cu/Gr/Cu)layered composites were investigated using ab initio calculations,and the results are compared to those in the bulk copper and pristine graphene.The results show that the formation energy of C vacancies in the Cu/Gr/Cu composite is smaller than that in pristine graphene due to the stretched C-C bond.The fcc site is most stable for Cu and C interstitials near the interface.The effect of the Cu/Gr/Cu interface on Cu interstitials is much stronger than that on C interstitials.The interface can act as a sink to trap Cu point defects.The sink strength of the interface for Cu defects is estimated to be about 15 ?.2.The migration mechanisms of point defects in the Cu/Gr/Cu composite were analyzed by the CI-NEB method.The results indicate that the migration energy barrier of a C vacancy in the graphene layer of Cu/Gr/Cu composite is lower than that in the pristine graphene.The Cu vacancy near the interface prefers to jump into the interface center.The Cu and C interstitials favorably jump between the two nearest fcc sites by passing through a hollow site.The migration of Cu interstitials in the interface is easier than in bulk Cu.3.The point defect properties of nickel/graphene/nickel(Ni/Gr/Ni)layered composite were also investigated using ab initio calculations.The results show that the formation energy of C vacancies in the Ni/Gr/Ni composite significantly decreases comparing to that in pristine graphene.In the Ni/Gr/Ni interface,the Ni interstitial at a hollow site is most stable.The effect of the interface on Ni interstitials is much stronger than that on C interstitials.The interface can trap Ni point defects within 12.5 ?4.The migration mechanisms of point defects in the Ni/Gr/Ni composite were analyzed by the CI-NEB method.The migration energy barrier of a C vacancy in the graphene layer of the composite is higher than that in the pristine graphene.The Ni interstitials may jump between the two nearest hollow sites by passing through a fcc site or jump directly.The migration of Ni interstitials in the interface is harder than in bulk Ni.5.The formation energies of C vacancies in the Cu/Gr/Cu and Ni/Gr/Ni composite are smaller than that in pristine graphene,but the reasons are different.Different metals in metal-graphene composite have different effect on the migration of C vacancies.The most stable interstitial site is the fcc site in Cu/Gr/Cu composite,but the hollow site in Ni/Gr/Ni composite.These two metal-graphene interfaces slightly affect the formation energy of C interstitials,but act as strong sinks for both metal interstitials and vacancies which verifies the radiation resistance of metal-graphene composite materials. |
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