The core structure of screw dislocations with [001] Burgers vector in Mg 2 SiO 4  olivine

Srinivasan Mahendran,Philippe Carrez,Patrick Cordier

doi:10.5802/crphys.27

Abstract

In this study, we report atomistic calculations of the core structure of screw dislocations with [001] Burgers vector in Mg2SiO4 olivine. Computations based on the THB1 empirical potential set for olivine show that the stable core configurations of the screw dislocations correspond to a dissociation in {110} planes involving collinear partial dislocations. As a consequence, glide appears to be favorable in {110} planes at low temperature. This study also highlights the difference between dislocation glide mechanism in {110} versus (010) or (100) for which glide is expected to occur through a locking–unlocking mechanism.

Highlights

Since the work of Peierls and his seminal paper entitled “The size of a dislocation” [1], it has been well established that the exact atomic arrangement in the vicinity of the dislocation core is a key issue in plasticity
Computations based on the THB1 empirical potential set for olivine show that the stable core configurations of the screw dislocations correspond to a dissociation in {110} planes involving collinear partial dislocations
Using deformation experiments performed at ambient pressure on polycrystalline olivine, Raleigh [26] showed that the deformation of olivine results from the activation of [001] glide at low temperature and relatively high-stress conditions, whereas above 1000 °C, Carter and Ave’Lallemant [31] observed activation of [100] slip

Summary

Introduction

Since the work of Peierls and his seminal paper entitled “The size of a dislocation” [1], it has been well established that the exact atomic arrangement in the vicinity of the dislocation core is a key issue in plasticity. It is worth noticing that previously mentioned intrinsic properties apply to more complex materials than simple metals, including, L12 alloys [17], oxides [18, 19], ceramics or minerals [20,21,22,23] Because of their importance to understand the nature of deformations in the Earth interior, the plastic properties of some minerals have been extensively studied. It is commonly accepted that [010] glide is not activated in olivine and that the plastic properties result from activation of two types of dislocations with [100] and [001] Burgers vectors, the two shortest lattice repeats of the lattice [25] This results from laboratory experiments [26,27,28,29], and from observations of natural samples made with optical microscopy or Transmission Electron Microscopy (TEM) techniques [30]. Based on electron tomography, the three possible slip planes, i.e. (100), (010), and {110}, have been reported simultaneously [37], but with a greater occurrence of {110}

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Discussion

Conclusion