The High-PT Body-Centered Cubic Iron in the Inner Core: Observed Yet Unnoticed.
Abstract
The solid inner core of the Earth is mostly iron. Therefore, the structure of the stable phase of iron under the Inner Core pressure temperature conditions is of ultimate importance for the explanation of Inner Core properties, such as high attenuation of seismic signal, low shear resistance, anisotropy, and differetial rotation to name a few. Recently, by the largest size wise ever DFT MD simulations of iron we confirmed the earlier embedded-atom based finding of thermodynamic stability of the body-centered cubic iron phase. The bcc Fe becomes more stable than the hcp iron at the temperatures above 5200 K at the pressure of 360 GPa (pressure in the center of the Earth). This prediction has been recently confirmed experimentally. This means, that the Inner Core is the bcc iron. However, there are a number of experiments that claim to not see the bcc iron at the conditions where the bcc iron was predicted to exist. In our simulations we observed that the bcc possess unique properties, the most remarkable is the liquid-like diffusion yet with the conservation of the crystalline structure. This diffusion leads to formation of liquid like features in experiments, besides the X-ray diffraction pattern consists of essentially just one (110) peak, while the rest forming a broad liquid like backgorund. I will demonstrate, that the computed properties allow a new interpretation of a number of experiments, where bcc was in fact observed, however the results of the experiment were misinterpreted. No problems with the results of the experiments - just with their interpretation. It is rather natural that many experimentalists have not recognized the bcc phase in their experiments- how one can recognize something if one does not know how that something looks like? The bcc phase explains all the enigmatic properties of the Inner Core, while the hcp phase does not explain any of them: high-PT hcp phase is an isotropic, low attenutating, high shear resistance phase - exact opposite of the bcc iron phase and of the Inner Core. Our study is a perfect example how the insight into the physics of a mineral allows a new interpretation of collected experimental data. These new interpretations consistently confirm the stability of the high-PT body-centered cubic phase in the Earth Inner Core.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR23A..05B
- Keywords:
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- 3904 Defects;
- MINERAL PHYSICS;
- 3909 Elasticity and anelasticity;
- MINERAL PHYSICS;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 3619 Magma genesis and partial melting;
- MINERALOGY AND PETROLOGY