Dislocation structure of deformed olivine single crystals from conventional EBSD maps

Abstract

Dislocations, linear defects in a crystalline lattice characterized by their slip systems, can provide a record of grain internal deformation. Comprehensive examination of this record has been limited by intrinsic limitations of the observational methods. Transmission electron microscopy reveals individual dislocations, but images only a few square $$\upmu$$ μ m of sample. Oxidative decoration requires involved sample preparation and has uncertainties in detection of all dislocations and their types. The possibility of mapping dislocation density and slip systems by conventional (Hough-transform based) EBSD is investigated here with naturally and experimentally deformed San Carlos olivine single crystals. Geometry and dislocation structures of crystals deformed in orientations designed to activate particular slip systems were previously analyzed by TEM and oxidative decoration. A curvature tensor is calculated from changes in orientation of the crystal lattice, which is inverted to calculate density of geometrically necessary dislocations with the Matlab Toolbox MTEX. Densities of individual dislocation types along with misorientation axes are compared to orientation change measured on the deformed crystals. After filtering (denoising), noise floor and calculated dislocation densities are comparable to those reported from high resolution EBSD mapping. For samples deformed in [110]c and [011]c orientations EBSD mapping confirms [100](010) and [001](010), respectively, as the dominant slip systems. EBSD mapping thus enables relatively efficient observation of dislocation structures associated with intracrystalline deformation, both distributed, and localized at sub-boundaries, over substantially larger areas than has previously been possible. This will enable mapping of dislocation structures in both naturally and experimentally deformed polycrystals, with potentially new insights into deformation processes in Earth’s upper mantle.

Using Misorientation and Weighted Burgers Vector Statistics to Understand Intragranular Boundary Development and Grain Boundary Formation at High Temperatures

“…For all the selected intragranular boundaries, the boundary misorientation axes and WBV across these boundaries have directions that are mostly clustering at rational crystallographic axes (Section 4.1), which are within or very close to the ice basal plane (Figures 6-10; Section 3). The alignment of WBV and/or misorientation axes near rational crystallographic axes are geometrically consistent with the dislocation model-a model in which boundaries are composed of dislocations with rational Burgers vectors (Faul, 2021;Linckens et al, 2016;Piazolo et al, 2015;Weikusat et al, 2017;Wheeler et al, 2009). WBVs across all selected intragranular boundaries have directions that are at 90° to misorientation axes (Section 4.3; Figures 6e, 7e, 7g, and 8e-10e), indicating that Burgers vectors lie sub-perpendicular to the rotation (misorientation) axes, as expected for the hexagonal crystal symmetry of ice (Hondoh, 2000;Nabarro, 1967).…”

Using crystal lattice distortion data for geological investigations: the Weighted Burgers Vector method

“…Equally, best fit/energy minimisation can be used on Hough based orientation data as in Pantleon (2008). In the latter case, even though there must be significant orientation errors that propagate through the calculations, results can be informative if acquisition conditions are optimised for angular precision (Faul, 2021). An approach like that used here could provide information how errors propagate.…”