scholarly journals Ni Doping: A Viable Route to Make Body-Centered-Cubic Fe Stable at Earth’s Inner Core

Minerals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 258
Author(s):  
Swastika Chatterjee ◽  
Sujoy Ghosh ◽  
Tanusri Saha-Dasgupta
Keyword(s):  
Inner Core ◽  
Computational Study ◽  
Stable Phase ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Ni Doping ◽  
Earth’S Inner Core ◽  
Core Condition ◽  
Theoretical Evidence ◽  
The Stability

With the goal of answering the highly debated question of whether the presence of Ni at the Earth’s inner core can make body-centered cubic (bcc) Fe stable, we performed a computational study based on first-principles calculations on bcc, hexagonal closed packed (hcp), and face-centered cubic (fcc) structures of the Fe1−xNix alloys (x = 0, 0.0312, 0.042, 0.0625, 0.084, 0.125, 0.14, 0.175) at 200–364 GPa and investigated their relative stability. Our thorough study reveals that the stability of Ni-doped bcc Fe is crucially dependent on the nature of the distribution of Ni in the Fe matrix. We confirm this observation by considering several possible configurations for a given concentration of Ni doping. Our theoretical evidence suggests that Ni-doped bcc Fe could be a stable phase at the Earth’s inner core condition as compared to its hcp and fcc counterparts.

scholarly journals Stability of body-centered cubic iron–magnesium alloys in the Earth's inner core

2009 ◽  
Vol 106 (37) ◽  
pp. 15560-15562 ◽  
Author(s):  
Krisztina Kádas ◽  
Levente Vitos ◽  
Börje Johansson ◽  
Rajeev Ahuja
Keyword(s):  
Inner Core ◽  
The Body ◽  
Mg Alloys ◽  
Functional Study ◽  
Body Centered Cubic ◽  
Calculated Density ◽  
The Core ◽  
Earth’S Inner Core ◽  
Core Conditions ◽  
Bcc Phase

The composition and the structure of the Earth's solid inner core are still unknown. Iron is accepted to be the main component of the core. Lately, the body-centered cubic (bcc) phase of iron was suggested to be present in the inner core, although its stability at core conditions is still in discussion. The higher density of pure iron compared with that of the Earth's core indicates the presence of light element(s) in this region, which could be responsible for the stability of the bcc phase. However, so far, none of the proposed composition models were in full agreement with seismic observations. The solubility of magnesium in hexagonal Fe has been found to increase significantly with increasing pressure, suggesting that Mg can also be an important element in the core. Here, we report a first-principles density functional study of bcc Fe–Mg alloys at core pressures and temperatures. We show that at core conditions, 5–10 atomic percent Mg stabilizes the bcc Fe both dynamically and thermodynamically. Our calculated density, elastic moduli, and sound velocities of bcc Fe–Mg alloys are consistent with those obtained from seismology, indicating that the bcc-structured Fe–Mg alloy is a possible model for the Earth's inner core.

High-pressure phase transitions and equations of state in NiSi. I.Ab initiosimulations

2012 ◽  
Vol 45 (2) ◽  
pp. 186-196 ◽  
Author(s):  
Lidunka Vočadlo ◽  
Ian G. Wood ◽  
David P. Dobson
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Inner Core ◽  
Equations Of State ◽  
Nickel Content ◽  
Stable Phase ◽  
First Principles Calculations ◽  
Cscl Structure ◽  
Earth’S Inner Core ◽  
Pressure Phase

First-principles calculations have been used to determine the equation of state and structural properties of NiSi up to pressures equivalent to that in the Earth's inner core. At atmospheric pressure, the thermodynamically stable phase is that with the MnP structure (as found experimentally). At high pressures, NiSi shows phase transformations to a number of high-pressure polymorphs. For pressures greater than ∼250 GPa, the thermodynamically stable phase of NiSi is that with the CsCl structure, which persists to the highest pressures simulated (∼500 GPa). At the pressures of the Earth's inner core, therefore, NiSi and FeSi will be isostructural and thus are likely to form a solid solution. The density contrast between NiSi and FeSi at inner-core pressures is ∼6%, with NiSi being the denser phase. Therefore, if a CsCl-structured (Fe,Ni)Si alloy were present in the inner core, its density (for the commonly assumed nickel content) might be expected to be ∼1% greater than that of pure FeSi.

scholarly journals Two-step nucleation of the Earth’s inner core

2022 ◽  
Vol 119 (2) ◽  
pp. e2113059119
Author(s):  
Yang Sun ◽  
Feng Zhang ◽  
Mikhail I. Mendelev ◽  
Renata M. Wentzcovitch ◽  
Kai-Ming Ho
Keyword(s):  
Molecular Dynamics ◽  
Inner Core ◽  
Nucleation Mechanism ◽  
Body Centered Cubic ◽  
Hexagonal Close Packed ◽  
Key Factor ◽  
Earth’S Inner Core ◽  
Core Conditions ◽  
Dynamics Simulations ◽  
Bcc Phase

The Earth's inner core started forming when molten iron cooled below the melting point. However, the nucleation mechanism, which is a necessary step of crystallization, has not been well understood. Recent studies have found that it requires an unrealistic degree of undercooling to nucleate the stable, hexagonal, close-packed (hcp) phase of iron that is unlikely to be reached under core conditions and age. This contradiction is referred to as the inner core nucleation paradox. Using a persistent embryo method and molecular dynamics simulations, we demonstrate that the metastable, body-centered, cubic (bcc) phase of iron has a much higher nucleation rate than does the hcp phase under inner core conditions. Thus, the bcc nucleation is likely to be the first step of inner core formation, instead of direct nucleation of the hcp phase. This mechanism reduces the required undercooling of iron nucleation, which provides a key factor in solving the inner core nucleation paradox. The two-step nucleation scenario of the inner core also opens an avenue for understanding the structure and anisotropy of the present inner core.

Voids in Irradiated Tungsten and Molybdenum

1969 ◽  
Vol 27 ◽  
pp. 190-191
Author(s):  
Robert C. Rau ◽  
Robert L. Ladd
Keyword(s):  
Melting Point ◽  
Fast Neutron ◽  
Neutron Irradiation ◽  
Elevated Temperatures ◽  
Irradiation Temperature ◽  
The Body ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Cubic Metals ◽  
Face Centered

Recent studies have shown the presence of voids in several face-centered cubic metals after neutron irradiation at elevated temperatures. These voids were found when the irradiation temperature was above 0.3 Tm where Tm is the absolute melting point, and were ascribed to the agglomeration of lattice vacancies resulting from fast neutron generated displacement cascades. The present paper reports the existence of similar voids in the body-centered cubic metals tungsten and molybdenum.

scholarly journals Irradiation Behaviors in BCC Multi-Component Alloys with Different Lattice Distortions

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 706
Author(s):  
Yue Su ◽  
Songqin Xia ◽  
Jia Huang ◽  
Qingyuan Liu ◽  
Haocheng Liu ◽  
...  
Keyword(s):  
Single Phase ◽  
Vacuum Arc ◽  
Face Centered Cubic ◽  
Body Centered Cubic ◽  
Chemical Complexity ◽  
Arc Melting ◽  
Vacuum Arc Melting ◽  
Lattice Distortions ◽  
Face Centered ◽  
Displacement Per Atom

Recently, the irradiation behaviors of multi-component alloys have stimulated an increasing interest due to their ability to suppress the growth of irradiation defects, though the mostly studied alloys are limited to face centered cubic (fcc) structured multi-component alloys. In this work, two single-phase body centered cubic (bcc) structured multi-component alloys (CrFeV, AlCrFeV) with different lattice distortions were prepared by vacuum arc melting, and the reference of α-Fe was also prepared. After 6 MeV Au ions irradiation to over 100 dpa (displacement per atom) at 500 °C, the bcc structured CrFeV and AlCrFeV exhibited significantly improved irradiation swelling resistance compared to α-Fe, especially AlCrFeV. The AlCrFeV alloy possesses superior swelling resistance, showing no voids compared to α-Fe and CrFeV alloy, and scarce irradiation softening appears in AlCrFeV. Owing to their chemical complexity, it is believed that the multi-component alloys under irradiation have more defect recombination and less damage accumulation. Accordingly, we discuss the origin of irradiation resistance and the Al effect in the studied bcc structured multi-component alloys.

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