Dislocations dynamics during plastic deformations of complex plasma crystals

Abstract

Summary form only given. Solids are known to have crystalline structures, which are often disrupted by defects. Among them, dislocations are topological defects representing permanent deviations of atoms from their ideal periodicity in the crystal. Dislocations define many properties of crystalline materials: the motion of dislocations at the microscopic scale is known to be responsible for macroscopic deformations of materials under applied stress by sliding motion of neighbouring atomic planes over each other [1]. Experimental observations of dislocations in real crystalline solids are very difficult. Here we use molecular dynamics simulation and an experimental model system - complex plasma to study dislocation motion. Complex plasmas consist of micron-sized plastic spheres or grains mixed with an ion-electron plasma. The microparticles are charged by collisions with the electrons and ions, predominantly negatively due to higher mobility of the electrons. These grains interact with each other electrostatically via a Yukawa potential and often form ordered structures. The experiments have been performed in a radio-frequency low pressure gas discharge, where a monolayer of plastic microspheres was suspended. The simulation was based on a Runge-Kutta integration of Newtonian equations of motion for each particle [2]. Here we report the results of experiments and numerical simulations of dislocations dynamics in complex plasma crystals submitted to a cycle of uniaxial compression and decompression. Under this external load the lattice undergoes structural rearrangement, in particular dislocations displacements and plastic deformations. Dislocations are observed to be generated, move in the lattice and disappear from the lattice during the cycle.