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Influence of Ni on the lattice stability of Fe-Ni alloys at multimegabar pressures
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
National University of Science and Technology MISIS, Russia .
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 22, 224107- p.Article in journal (Refereed) Published
Abstract [en]

The lattice stability trends of the primary candidate for Earths core material, the Fe-Ni alloy, were examined from first principles. We employed the exact muffin-tin orbital method (EMTO) combined with the coherent potential approximation (CPA) for the treatment of alloying effects. It was revealed that high pressure reverses the trend in the relative stabilities of the body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal close-packed (hcp) phases observed at ambient conditions. In the low pressure region the increase of Ni concentration in the Fe-Ni alloy enhances the bcc phase destabilization relative to the more close-packed fcc and hcp phases. However, at 300 GPa (Earths core pressure), the effect of Ni addition is opposite. The reverse of the trend is associated with the suppression of the ferromagnetism of Fe when going from ambient pressures to pressure conditions corresponding to those of Earths core. The first-principles results are explained in the framework of the canonical band model.

Place, publisher, year, edition, pages
American Physical Society , 2012. Vol. 86, no 22, 224107- p.
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-86890DOI: 10.1103/PhysRevB.86.224107ISI: 000312064300001OAI: diva2:583049

Funding Agencies|Swedish Research Council (VR)|621-2008-55352011-42-59|Goran Gustafsson Foundation for Research in Natural Sciences and Medicine||Swedish Government Strategic Research Area Grant in Materials Science||Functional Materials and VR Linnaeus Grant LiLi-NFM||Swedish Foundation for Strategic Research through the SRL program||Ministry of Education and Science of the Russian Federation|14.B37.21.089014.A18.21.0893|Russian Foundation for Basic Researches|10-02-00-194a|Swedish National Infrastructure for Computing SNIC||

Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2013-09-11
In thesis
1. Influence of stresses and impurities on thermodynamic and elastic properties of metals and alloys from ab initio theory
Open this publication in new window or tab >>Influence of stresses and impurities on thermodynamic and elastic properties of metals and alloys from ab initio theory
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Stresses and impurities may influence elastic properties, phase stability and magnetic behavior of metals and their alloys. A physical understanding of this influence is of great importance to both fundamental science and technological applications. The diverse methods used in this work allowed us to shed light on the various aspects of the problem. In particular, in this work the thermodynamic, magnetic and elastic properties of Fe and Fe-Ni alloys at Earth’s inner core conditions were investigated by means of the ab initio theory. The main features of these calculations are on one side the extreme pressure-temperature conditions; on the other side the strong-correlation effects, which at these conditions may play an unexpected role. That is why I used different approaches, ranging from molecular dynamics to the dynamical mean field theory.

Interesting possibility for the effect of non-hydrostatic stresses on the stability of the body-centered cubic (bcc) phase of iron was observed. If detected, it could allow for an explanation of striking contradictions in high-pressure experiments. The influence of the alloying with Ni on the stability of Fe was studied. It was shown that the observed reverse of the stability trend under pressure is associated with the suppression of ferromagnetism at conditions of Earth’s inner core.

The strong correlation effects were observed in Fe3Ni by means of the dynamical mean field theory, revealing that the local environment of iron atoms is crucial for the strength of the on-site electronic correlations.

There is also an exciting experimental finding of our colleagues indicating that magnetism in pure nickel survives at very high pressures up to 260 GPa, i.e. up to the highest pressure at which magnetism in any material has ever been observed. Our calculations of the pressure dependence of the effective exchange interaction parameter and the hyperfine field support the picture of the ordered ferromagnetic state in Ni at multimegabar pressures.

Further, hydrogen is believed to be an important light impurity in Earth’s core. Thereupon the hydrogen containing FeOOH was also investigated. The prediction of the effect of symmetrization of the hydrogen bond under pressure was made.

The universality of applied methods allowed us to study the elastic constants of TiN, which is of high relevance to the industry of cutting tools. The importance of taking into account the finite temperature effects in the calculations of the elastic properties was demonstrated. Another case of practical interest is the Fe-Cr system, a prototype of many industrial steels. For instance, it is used in cooling pipes of pressure vessel reactors. We studied the effect of hydrostatic pressure on the phase stability of Fe-Cr alloys and revealed intriguing differences in the ordering tendencies depending on the Cr concentration and magnetic state of the alloy. We showed how variation of the ordering tendency between the Fe and Cr atoms emerges due to suppression of the local magnetic moment on the Cr atoms.

Noteworthy, hydrogen is not only the basic material playing fundamental role on and in the Earth, it is also a very promising source of fuel, which does not pollute the environment. In this sense the problem of hydrogen storage in Pd is of separate but related interest and it was theoretically investigated in the present work. The effect of vacancies on the energetically preferable position of hydrogen in the Pd cell was addressed. My theoretical results supported the experimental suggestion of multiple occupation of Pd vacancies by hydrogen.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. 85 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1531
National Category
Condensed Matter Physics
urn:nbn:se:liu:diva-97383 (URN)978–91–7519–557–5 (print) (ISBN)
Public defence
2013-09-19, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2013-09-13Bibliographically approved

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