Using multigrain crystallography to identify the onset of plastic yielding and stress-state in mantle minerals.

Abstract:

The introduction of multigrain crystallography (MGC) applied in a diamond anvil cell (DAC) has provided new insights into microstructural evolution of materials in extreme conditions, allowing for simultaneous investigations including structure refinement, new phase identification, and orientation relations across phase transitions in a single experiment. In this study we add to this list of capabilities by combining the newly enhanced detector capability of the Advanced Light Source (ALS) with MGC’s ability to track individual diffraction intensities from several unique grains at high pressure to identify lattice planes responsible for the onset of plastic yielding; a key component to understanding the evolution of materials in Earth's lower mantle. We test this method on a naturally occurring olivine sample, a mineral whose deformation mechanisms have been extensively studied across a range of conditions and when combined with its low crystal symmetry, an ideal candidate for this method. Furthermore, we resolve the stress state in individual grains at the onset of yielding as well as the global equivalent stress and strain within the analyzed region of the sample. We provide validation of this technique through comparisons to measurements under similar conditions and show the MGC can be used as an all-encompassing method to explore material behavior in extreme conditions.