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An ab initio molecular dynamics study of iron phases at high pressure and temperature
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2011 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 23, no 48, 485402- p.Article in journal (Refereed) Published
Abstract [en]

The crystal structure of iron, the major component of the Earth's inner core (IC), is unknown for the IC high pressure (P; 3.3-3.6 Mbar) and temperature (T; 5000-7000 K). There is mounting evidence that the hexagonal close-packed (hcp) phase of iron, stable at the high P of the IC and a low T, might be unstable under the IC conditions due to the impact of high T and impurities. Experiments at the IC P and T are difficult and do not provide a conclusive answer as regards the iron stability at the pressure of the IC and temperatures close to the iron melting curve. Recent theory provides contradictory results regarding the nature of the stable Fe phase. We investigated the possibility of body-centered cubic (bcc) phase stabilization at the P and T in the vicinity of the Fe melting curve by using ab initio molecular dynamics. Thermodynamic calculations, relying on the model of uncorrelated harmonic oscillators, provide nearly identical free energies within the error bars of our calculations. However, direct simulation of iron crystallization demonstrates that liquid iron freezes in the bcc structure at the P of the IC and T = 6000 K. All attempts to grow the hcp phase from the liquid failed. The mechanism of bcc stabilization is explained. This resolves most of the earlier confusion.

Place, publisher, year, edition, pages
2011. Vol. 23, no 48, 485402- p.
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-167205DOI: 10.1088/0953-8984/23/48/485402ISI: 000298141600016OAI: oai:DiVA.org:uu-167205DiVA: diva2:481870
Available from: 2012-01-23 Created: 2012-01-23 Last updated: 2012-01-23Bibliographically approved

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Arapan, Sergiu
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Materials Theory
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