Effect of interatomic potentials on mass transfer by supersonic 2-crowdions

Abstract

An interstitial atom placed into a close-packed atomic row is called crowdion. Crowdions are very efficient in mass transfer in the crystal lattice since they are highly mobile, soliton-like objects. It has been demonstrated recently that single interstitial atom can move along a close-packed atomic row with a supersonic speed in two different modes, either as a classical 1-crowdion or as a 2-crowdion. The difference is that in the latter case two atoms move with a high speed at the same time, while in the former case only one atom has high speed. It has been shown that the 2-crowdion requires lesser energy to initiate mass transfer and it travels longer distance if it has same energy with the 1-crowdion. It is important to compare the efficiency of mass transfer by 2-crowdions in different materials. Materials have different properties because the interatomic interactions between various atoms are different. In the present study we demonstrate that the most important characteristic of the interatomic potentials, that has effect on the crowdion path length, is the energy of the interatomic bond at the distance between two atoms equal to a half of the equilibrium interatomic distance. This conclusion is justified by the condition of self-focusing propagation of supersonic crowdions, that is the collision velocity of the atoms should not exceed the value when they approach each other closer than half interatomic distance. As an example, mass transfer by 1-and 2-crowdions is considered in two-dimensional triangular lattice with Morse and Born-Mayer potentials.