TIMEleSS Multigrain Wiki

TIMEleSS Multigrain WikiMultigrain X-ray diffraction (sometimes called 3D-XRD or HEDM depending on communities) allows characterizing hundreds of crystals in a polycrystalline material. It has been adapted to diamond anvil cell experiments for the investigation of materials under high pressure and high temperature. The method lies at the core of the experimental portion of the TIMEleSS project. We use it to characterize transformation and deformation microstructures in mantle minerals.

Multigrain X-ray diffraction can be hard to learn and implement. Hence, along the course of the project, timeless members documented their procedures for processing such data in an online documentation: the TIMEleSS Multigrain Wiki.

We are now finished with our rounds of experiments, data has been processed, and results are being submitted for publication, so it is time to give back to the community! The TIMEleSS Multigrain Wiki has been accessible for years to who knew the URL. Now the link is public and should be easy to find with your best search engines. Please use it, enjoy it, and do not hesitate to contact us if you want to contribute and suggest corrections

This wiki, among with other outputs, was used as a basis for the creation of the Commission on Diffraction Microstructure Imaging of the International Union of Crystallography. This new Commission on Diffraction Microstructure Imaging was established at the Prague General Assembly in August 2021 and TIMEleSS PI S. Merkel is one of the founding members for the application.

New publication in Frontiers in Earth Science

Deformation of Polycrystalline MgO Up to 8.3 GPa and 1270 K: Microstructures, Dominant Slip-Systems, and Transition to Grain Boundary SlidingWe have a new publication! On May 9th, 2022, former TIMEleSS PhD student Estelle Ledoux published a new paper in Frontiers in Earth Science: Deformation of Polycrystalline MgO Up to 8.3 GPa and 1270 K: Microstructures, Dominant Slip-Systems, and Transition to Grain Boundary Sliding.

The work is a result of a collaboration between the Université de Lille and the University of Utah. We focus on polycrystalline periclase, the pure Mg end-member of the second-most abundant mineral in the Earth lower mantle, ferro-periclase, for which mechanical properties are important to understand flow and the dynamics of the Earth mantle.

we deform polycrystalline periclase at conditions ranging from 1.6 to 8.3 GPa and 875–1,270 K. We analyse the flow laws and microstructures of the recovered samples using electron microscopy and compare our observations with predictions from the literature. We identify a first mechanism for samples deformed at 1,270 K, attributed to a regime controlled by grain boundary sliding accommodated by diffusion, and characterized by a small grain size, an absence of texture, and no intracrystalline deformation. At 1,070 K and below, the deformation regime is controlled by dislocations. The samples show a more homogeneous grain size distribution, significant texture, and intracrystalline strains. In this regime, deformation is controlled by the ⟨110⟩{110} slip system and a combined ⟨110⟩{110} and ⟨110⟩{100} slip, depending on pressure and temperature.

Based on these results, we propose an updated deformation map for polycrystalline MgO at mantle conditions and discuss the implications for ferropericlase and seismic observations in the Earth’s lower mantle.

More details can be found in the open-access full reference of the study: E. E. Ledoux, F. Lin, L. Miyagi, A. Addad,  A. Fadel, D. Jacob, F. Béclin, and S. Merkel. Deformation of Polycrystalline MgO Up to 8.3 GPa and 1270 K: Microstructures, Dominant Slip-Systems, and Transition to Grain Boundary Sliding. Front. Earth Sci. 10, 849777 (2022) [doi: 10.3389/feart.2022.849777]

We are hiring!

Post-doc position on wave propagation in structures and microstructures at the University of Lille, France

The TIMEleSS project is looking for a post-doctoral fellow. The position is available for 1 year and extendable. The position is attached to the Earth and Planetary Materials group the Unité Matériaux et Transformations, at the Université de Lille, France, with strong collaborations with the Institute for Geophysics at the University of Münster.

The post-doc will be in charge of  simulating wave propagation in structures and microstructures with the aim of interpreting deep Earth seismic observables.

The candidate should have a strong background in deep Earth seismology and/or wave propagation in complex media and/or mineral physics and will be in charge of connecting mineral physics knowledge of phase transformations and microstructures in the Earth’s mantle to potential observations of seismic reflections and scattering.

Details on the position, conditions, and requirements can be found in the following document. The review of of applications will start by January 31st 2020 and will continue until the position is filled. The position is expected to start in the spring or the summer of 2020.