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Theoretical Considerations of Local Environment Effects in Alloys
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is devoted to a theoretical study of local environment effects in alloys. A fundamental property of a disordered system is that all chemically equivalent atoms are different due to their different chemical environments, in contrast to an ideal periodic solid where all the atoms that occupy equivalent positions in the crystal have exactly the same physical properties. The local environment effects have been largely ignored in earlier theories of disordered systems, that is the system has been treated as a whole and average properties have been derived. Moreover, inhomogeneous systems, such as surfaces and interfaces, induce local environment effects that are not necessarily present in the bulk.

The importance and presence of local environment effects are illustrated by calculating observable physical properties in various systems. In particular, by employing the complete screening picture the effects of local environments on the core-level binding energy shifts as well as Auger shifts in random alloys are in- vestigated. This so-called disorder broadening effect has recently been observed experimentally. It is shown that there are different contributions to the disorder broadening that vary with the local chemical environment. Furthermore, the influ- ence of inhomogeneous lattice distortions on the disorder broadening of the core- level photoemission spectra are considered for systems with large size-mismatch between the alloy components.

The effects of local chemical environments on physical properties in magnetic systems are illuminated. A noticeable variation in the electronic structure, local magnetic moments and exchange parameters at different sites is obtained. This reflects the sensitivity to different chemical environments and it is shown to be of qualitative importance in the vicinity of magnetic instability.

The local environment effects due to the presence of surfaces and interfaces are also considered. The effect is explicitly studied by considering the concentration profile of a thin Ag-Pd film deposited on a Ru substrate. Two computational approaches are utilized to calculate the relative composition in each layer of the thin film as a function of temperature in a theoretically consistent way. It is shown that, opposed to the situation in the bulk, where a complete solubility between Ag and Pd takes place, a non-uniform distribution of the alloy components across the film is observed.

In another study it is investigated whether the presence of TiN interfaces changes the dynamical and thermodynamic stability of B1 SiN. Phonon calcula- tions show that TiN interfaces have a stabilization effect on the lattice dynamics. On the other hand, calculations of the Si vacancy formation energy show that the structures are unstable with respect to composition variations.

 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2010. , 86 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1353
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-63443ISBN: 978-91-7393-285-1 (print)OAI: oai:DiVA.org:liu-63443DiVA: diva2:379745
Public defence
2010-12-17, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2010-12-27 Created: 2010-12-19 Last updated: 2010-12-27Bibliographically approved
List of papers
1. Ab initio study of disorder broadening of core photoemission spectra in random Cu-Pd and Ag-Pd alloys
Open this publication in new window or tab >>Ab initio study of disorder broadening of core photoemission spectra in random Cu-Pd and Ag-Pd alloys
2005 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 5Article in journal (Refereed) Published
Abstract [en]

A first-principles study of the effect of local environment on the electronic structure of random face-centered cubic Ag-Pd and Cu-Pd alloys is presented. The core-level shift for each atom in the equiatomic alloys is calculated and compared to experimental data. It is shown how the initial-state and final-state distributions contribute to the total broadening. We find that the initial-state and the final-state contributions together increase the broadening for the investigated core levels in Cu and Ag, whereas they cancel each other to a large degree for Pd. We also demonstrated how local lattice relaxations influence the binding energy shift. We find that relaxation does not influence the average shift, though it is able to affect the broadening of the simulated x-ray photoelectron spectroscopy spectra. © 2005 The American Physical Society.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-29016 (URN)10.1103/PhysRevB.72.054210 (DOI)14255 (Local ID)14255 (Archive number)14255 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
2. Local environment effects in random metallic alloys
Open this publication in new window or tab >>Local environment effects in random metallic alloys
2005 (English)In: The Science of Complex Alloy Phases: proceedings of a symposium held during the TMS Annual Meeting and Exhibition in San Francisco, California, USA, February 13-17, 2005, to honor the Wiliam Hume-Rothery Award recipient Professor Uichiro Mizutani / [ed] Thaddeus B. Massalski and Patrice E. A. Turchi, USA: TMS , 2005, 1, 87-108 p.Chapter in book (Other academic)
Abstract [en]

This book is published in honor of the 2005 Hume-Rothery Award Recipient, Uichiro Mizutani. It emphasizes both theoretical and experimental aspects of electronic, structural, and thermodynamic properties of complex alloy phases. Leading experts provide an assessment of our current understanding of the structural properties of complex materials, including quasicrystalline and amorphous alloys. Special emphasis is placed on our understanding of why nature is able to stabilize complex atomic arrangements and on recent results related to structurally complex alloy phases. These topics, in the spirit of the work carried out by U. Mizutani, constitute the main theme of the book

Place, publisher, year, edition, pages
USA: TMS, 2005 Edition: 1
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-24462 (URN)6574 (Local ID)0-87339-593-X (ISBN)978-0-87339-593-9 (ISBN)6574 (Archive number)6574 (OAI)
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-09-26Bibliographically approved
3. Core-level shifts in complex metallic systems from first principle
Open this publication in new window or tab >>Core-level shifts in complex metallic systems from first principle
2006 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 243, no 11, 2447-2464 p.Article in journal (Refereed) Published
Abstract [en]

We show that core-level binding energy shifts (CLS) can be reliably calculated within density functional theory. The scheme includes both the initial (electron energy eigenvalue) as well as final state (relaxation due to core-hole screening) effects in the same framework. The results include CLS as a function of composition in substitutional random bulk and surface alloys. Sensitivity of the CLS to the local chemical environment in the bulk and at the surface is demonstrated. A possibility to use the CLS for structural determination is discussed. Finally, an extension of the model is made for Auger kinetic energy shift calculations.

Place, publisher, year, edition, pages
Wiley, 2006
Keyword
71.15.-m, 71.23.-k, 79.20.Fv, 79.60.Dp, 79.60.Ht, 79.60.Jv
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-37239 (URN)10.1002/pssb.200642165 (DOI)34061 (Local ID)34061 (Archive number)34061 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
4. Suppression of disorder broadening of core-level photoelectron lines in CuAu alloys by inhomogeneous lattice distortion
Open this publication in new window or tab >>Suppression of disorder broadening of core-level photoelectron lines in CuAu alloys by inhomogeneous lattice distortion
Show others...
2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 1, 012201- p.Article in journal (Refereed) Published
Abstract [en]

Disorder broadening of core-level binding energies is a general effect observed in random alloys, and identifies an opportunity for studying specific local environments experimentally. Here we study it in an archetypical system: face-centered-cubic Cu50Au50. While the disorder broadening is clearly detectable at Au, at Cu it is below the detection limit. We supplement experiments by a theoretical study where we model the alloy by a large supercell constructed as a special quasirandom structure and calculate binding-energy shifts at all sites in the supercell. Theory shows that the suppression of the disorder broadening at Cu results from a delicate balance between the influence of local chemical environment and inhomogeneous lattice distortions on the site-resolved core-level shifts. Surprisingly, even larger relaxation-induced shifts are observed at Au sites.

Keyword
copper alloys, core levels, electronic structure, gold alloys, photoelectron spectra
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16832 (URN)10.1103/PhysRevB.79.012201 (DOI)
Available from: 2009-02-21 Created: 2009-02-20 Last updated: 2017-12-13Bibliographically approved
5. First principle calculations of core-level binding energy and Auger kinetic energy shifts in metallic solids
Open this publication in new window or tab >>First principle calculations of core-level binding energy and Auger kinetic energy shifts in metallic solids
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2010 (English)In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 178, no Sp. Iss. SI, 88-99 p.Article in journal (Refereed) Published
Abstract [en]

We present a brief overview of recent theoretical studies of the core-level binding energy shift (CLS) in solid metallic materials. The focus is on first principles calculations using the complete screening picture, which incorporates the initial (ground state) and final (core-ionized) state contributions of the electron photoemission process in X-ray photoelectron spectroscopy (XPS), all within density functional theory (DFT). Considering substitutionally disordered binary alloys, we demonstrate that on the one hand CLS depend on average conditions, such as volume and overall composition, while on the other hand they are sensitive to the specific local atomic environment. The possibility of employing layer resolved shifts as a tool for characterizing interface quality in fully embedded thin films is also discussed, with examples for CuNi systems. An extension of the complete screening picture to core-core-core Auger transitions is given, and new results for the influence of local environment effects on Auger kinetic energy shifts in fcc AgPd are presented.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2010
Keyword
Core-level shift, Disordered materials, Metallic alloys, Auger kinetic energy
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-57401 (URN)10.1016/j.elspec.2009.10.007 (DOI)000278295900006 ()
Note
Original Publication: Weine Olovsson, Tobias Marten, Erik Holmstrom, Borje Johansson and Igor Abrikosov, First principle calculations of core-level binding energy and Auger kinetic energy shifts in metallic solids, 2010, JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, (178), Sp. Iss. SI, 88-99. http://dx.doi.org/10.1016/j.elspec.2009.10.007 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2010-06-18 Created: 2010-06-18 Last updated: 2017-12-12Bibliographically approved
6. Magnetism in systems with reduced dimensionality and chemical disorder: the local environment effects
Open this publication in new window or tab >>Magnetism in systems with reduced dimensionality and chemical disorder: the local environment effects
2006 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 300, no 1, 211-215 p.Article in journal (Refereed) Published
Abstract [en]

We study influence of the local chemical environment, the so-called local environment effects, on the electronic structure and properties of magnetic systems with reduced dimensionality and chemical disorder, and show that they play a crucial role in a vicinity of magnetic instability. As a model, we consider Fe–Ni Invar. We present results obtained from ab initio calculations of the electronic structure, magnetic moments, and exchange interactions in random fcc Fe–Ni alloy, for a single monolayer alloy film on a Cu (0 0 1) substrate as well as in the bulk. We analyze the difference between the film and the bulk magnetization, which is found to be most pronounced for dilute alloys. We also analyze a sensitivity of the individual magnetic moments and effective exchange parameters to the local chemical environment of the atoms.

Place, publisher, year, edition, pages
Elsevier, 2006
Keyword
Local environment effects, Invar alloys, First-principles calculations
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17428 (URN)10.1016/j.jmmm.2005.10.065 (DOI)
Available from: 2009-03-24 Created: 2009-03-24 Last updated: 2017-12-13
7. Double-segregation effect in AgxPd1−x /Ru(0001) thin film nanostructures
Open this publication in new window or tab >>Double-segregation effect in AgxPd1−x /Ru(0001) thin film nanostructures
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2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, 125406-1-125406-7 p.Article in journal (Refereed) Published
Abstract [en]

We study the structural properties of ultrathin AgxPd1−x films on top of a Ru(0001) substrate. Effective interatomic interactions, obtained from first-principles calculations, have been used in Monte Carlo simulations to derive the distribution of the alloy components in a four-monolayer (4-ML) Ag-Pd film. Though Ag-Pd alloys show complete solubility in the bulk, the thin film geometry leads to a pronounced segregation between Ag and Pd atoms with a strong preference of Ag atoms toward the surface and Pd atoms toward the interface. The theoretical prediction of this double-segregation effect is strongly supported by photoelectron spectroscopy experiments carried out for 4-ML thin films. We also show, in an additional experiment, that even in the case where initially 1 ML Ag is buried under 6 ML Pd, the whole Ag ML segregates to the surface.

Place, publisher, year, edition, pages
APS, 2008
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-44362 (URN)10.1103/PhysRevB.77.125406 (DOI)76396 (Local ID)76396 (Archive number)76396 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13Bibliographically approved
8. Single-monolayer SiNx embedded in TiN: A first-principles study
Open this publication in new window or tab >>Single-monolayer SiNx embedded in TiN: A first-principles study
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 21, 212102- p.Article in journal (Refereed) Published
Abstract [en]

The dynamical and thermodynamic stability of a single monolayer of SiNx sandwiched isostructurally between B1-TiN(001) and (111) oriented slabs are investigated by means of density functional theory. Possible dynamical stabilization of the (001) interface, by distortion of the Si-N bonds, is considered and found to almost, but not completely, remove the phonon instabilities. The (111) interface on the other hand is found to be dynamically stable. We furthermore relax the stoichiometry degree of freedom by allowing for Si vacancies in the lattice and show that the ideal 1:1 SiN stoichiometry in both interfaces are thermodynamically unstable with respect to Si vacancy formation regardless if the system is grown under nitrogen-rich or nitrogen-poor conditions, and therefore ruling out its relevance for performance of real materials.

Place, publisher, year, edition, pages
American Physical Society, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-58256 (URN)10.1103/PhysRevB.81.212102 (DOI)000279381800001 ()
Note
Original Publication: Tobias Marten, Eyvas Isaev, Björn Alling, Lars Hultman and Igor Abrikosov, Single-monolayer SiNx embedded in TiN: A first-principles study, 2010, Physical Review B. Condensed Matter and Materials Physics, (81), 21, 212102. http://dx.doi.org/10.1103/PhysRevB.81.212102 Copyright: American Physical Society http://www.aps.org/ Available from: 2010-08-10 Created: 2010-08-09 Last updated: 2017-12-12Bibliographically approved

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