Crowdion mechanisms of self-diffusion in a two-dimensional crystal of metal

Full text: Crowdion mechanisms of self-diffusion in two-dimensional crystal of Ni, Al, Cu, Au were studied by the method of molecular dynamics. Interatomic interactions were given by Morse pair potential functions. The packing of atoms was corresponds to the plane <111> FCC lattice. Crowdions are the displacements of group of atoms along one of crystallographic directions. The activation energy of defects was calculated for the definite number of the displaced atoms, because a crowdion can contain variable number of atoms. Activation energy of crowdion Egr was calculated as the difference between the energy of crystal, containing the crowdion, and energy of ideal crystal. The energy Egr was calculated after relaxation and further cooling to 0 K of the calculated cell. The energy of thermal collective displacements of atoms, necessary for the formation of crowdions, was calculated. The final stage of the development of crowdion mechanism is the stage when substitution defect forms in the direction of the movement of crowdion and vacancy forms behind the final position of crowdion. To calculate the energy of crowdion QF, which can form similar pair of Frenkel, vacancy was generated in the calculated cell and the introduced atom was formed at several atoms along closely packed direction. One atom in crowdion was not allowed to move at the dynamic relaxation to prevent the process of annihilation of Frenkel pair. The values of activation energy of separate elements are shown in the tabular form