Supersonic N -Crowdions in a Two-Dimensional Morse Crystal
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Supersonic N-Crowdions in a Two-Dimensional Morse Crystal S. V. Dmitrieva,b,*, E. A. Korznikovaa, and A. P. Chetverikovc aInstitute
for Metal Superplasticity Problems, Russian Academy of Sciences, ul. Stepana Khalturina 39, Ufa, 450001 Russia b National Research Tomsk State University, pr. Lenina 36, Tomsk, 634050 Russia c Saratov National Research State University, Astrakhanskaya ul. 83, Saratov, 410012 Russia *e-mail: [email protected] Received November 1, 2017
Abstract—An interstitial atom placed in a close-packed atomic row of a crystal is called crowdion. Such defects are highly mobile; they can move along the row, transferring mass and energy. We generalize the concept of a classical supersonic crowdion to an N-crowdion in which not one but N atoms move simultaneously with a high velocity. Using molecular dynamics simulations for a close-packed two-dimensional Morse crystal, we show that N-crowdions transfer mass much more efficiently, because they are capable of covering large distances while having a lower total energy than that of a classical 1-crowdion. DOI: 10.1134/S1063776118030019
1. INTRODUCTION The mass transfer by point defects in crystalline solids is responsible for many of the physical processes that occur during plastic deformation [1–7], thermal treatment [8], and irradiation [9–13]. The motion of vacancies is the main mechanism of thermally activated diffusion [8]. Interstitial atoms have a higher energy and, consequently, their concentration in thermal equilibrium is much lower than that of vacancies, but their role increases significantly in nonequilibrium processes. Interstitial atoms can be immobile [14] or mobile, when they are located in close-packed atomic rows [15]; in the latter case, they are called crowdions. Interestingly, crowdions usually have a lower potential energy than that of immobile interstitials [15, 26]. Crowdions can be at rest, but they can also move with both subsonic and supersonic speeds [17–19]. Immobile or subsonic crowdions have the profile of a kink whose width is about ten atoms in a closepacked atomic row. Supersonic crowdions are highly localized on one or two atoms [19, 20]. Crowdions play a very important role in crystals in the relaxation processes associated with the mass and energy transfer [6, 21–28]. The irradiation of metals by slow neutrons and other particles gives rise to crystalline defects in them in the form of clusters of interstitials or vacancies. The clusters of interstitials were shown to be highly mobile [21–28]. The interest in investigating moving excitations in crystals has recently increased in connection with the experimentally detected annealing of defects deep inside a germanium single crystal under surface plasma treatment [29] and in connection with the
study of particle tracks visible in mica crystals by the naked eye [19, 30–34]. Discrete breathers [35–38] and crowdions [19] were considered as moving excitations in mica. The dynamics and collisions of supersonic crowdions in a two-dimensional lattice we
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