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Elastic constants and anisotropy in FeNi alloys at high pressures from first-principles calculations
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
Royal Institute of Technology.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
2009 (Engelska)Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, nr 21, s. 214112-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The single-crystal and polycrystalline elastic constants and the elastic anisotropy in face-centered cubic and hexagonal close-packed FeNi alloys have been investigated at ultrahigh pressures by means of first-principles calculations using the exact muffin-tin orbitals method and the coherent-potential approximation. Comparisons with earlier calculations for pure Fe and experimental results are presented and discussed. We show that Ni alloying into Fe increases slightly the density and has very little effect on bulk moduli. Moreover, the relative decrease in c(44) elastic constant is much stronger in the hcp phase than in the fcc one. It is found that the elastic anisotropy is higher for face-centered cubic than for the hexagonal close-packed structure of FeNi, even though the face-centered cubic phase has a higher degree of symmetry. The anisotropy in face-centered cubic structure decreases with increasing nickel concentration while a very weak increase is observed for the hexagonal close-packed structure.

Ort, förlag, år, upplaga, sidor
2009. Vol. 79, nr 21, s. 214112-
Nationell ämneskategori
Naturvetenskap
Identifikatorer
URN: urn:nbn:se:liu:diva-20159DOI: 10.1103/PhysRevB.79.214112OAI: oai:DiVA.org:liu-20159DiVA, id: diva2:233670
Tillgänglig från: 2009-09-01 Skapad: 2009-08-31 Senast uppdaterad: 2017-12-13
Ingår i avhandling
1. Effects of disorder in metallic systems from First-Principles calculations
Öppna denna publikation i ny flik eller fönster >>Effects of disorder in metallic systems from First-Principles calculations
2010 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

In this thesis, quantum-mechanical calculations within density-functional theory on metallic systems are presented. The overarching goal has been to investigate effects of disorder. In particular, one of the properties investigated is the bindingenergy shifts for core electrons in binary alloys using different theoretical methods. These methods are compared with each other and with experimental results. One such method, the so-called Slater-Janak transition state method relies on the assumption that the single-particle eigenvalues within density-functional theory are linear functions of their respective occupation number. This assumption is investigated and it is found that while the eigenvalues to a first approximation show linear behavior, there are also nonlinearities which can influence the core-level binding energy shifts.

Another area of investigation has been iron based alloys at pressures corresponding to those in the Earth’s inner core. This has been done for the hexagonal close packed and face entered cubic structures. The effects of alloying iron with magnesium and nickel on the equation of state as well on the elastic properties have been investigated. The calculations have shown that the hexagonal close packed structure in FeNi is more isotropic than the face-centered cubic structure, and that adding Mg to Fe has a large impact on the elastic properties.

Finally, the effects of disorder due to thermal motion of the atoms have been investigated through ab-initio molecular dynamics simulations. Within the limits of this method and the setup, it is found that the face-centered cubic structure of molybdenum can be dynamically stabilized at high temperature, leading to a metastable structure, on the average. The dynamical stabilization of face-centered cubic molybdenum also rendered it possible to accurately calculate the lattice stability relative to the body-centered cubic phase. Inclusion of temperature effects for the lattice stability using ab-initio molecular dynamics simulations resolves the disagreement between ab-initio calculations and thermochemical methods.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2010. s. 126
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1299
Nyckelord
Iron, Nickel, Magnesium, Manganese, Molybdenum, Zirconium, Elastic Constants, High pressure, Earth's core, Density-functional theory, Ab-initio, First-Principles, Core-level shifts, Molecular Dynamics, Phonons, Dynamical Instability
Nationell ämneskategori
Den kondenserade materiens fysik Annan fysik
Identifikatorer
urn:nbn:se:liu:diva-53584 (URN)978-91-7393-445-9 (ISBN)
Disputation
2010-03-12, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2010-02-11 Skapad: 2010-01-25 Senast uppdaterad: 2010-03-29Bibliografiskt granskad

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