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Amorphous and crystalline functional materials from first principles
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with various functional materials from first-principles methods and is divided into two major parts according to the underlying atomic structure of the system under study. The first part of the thesis deals with the temperature-induced structural phase transitions in metallic  β'-AuZn and perovskite oxide LiOsO3. The former one, i.e. binary AuZn, belongs to a class of shape-memory alloys that regain their initial shape due to a reversible martensitic phase transformation. Here, by means of density functional and density functional perturbation theories, we show that the martensitic transition is due to coupling between the Fermi surface nesting and anomalies in the phonon dispersion relations. The other metallic system, perovskite LiOsO3, exhibits a ferroelectric-like transition and is currently the first and sole realization of the Anderson and Blount idea. By means of ab initio molecular dynamics simulations, we investigate the mechanism behind this structural phase transformation.

Another part of the thesis is dedicated to modelling and characterization of topologically disordered materials on atomic level. The structural and electronic properties of amorphous W-S-N are addressed regarding its outstanding tribological properties, i.e. almost vanishing friction coefficient. Molecular dynamics “melt-and-quench” technique has been employed in order to construct a model structure of amorphous W-S-N. Further analysis of the atomic structure revealed a formation of quasi-free N2 molecules trapped in S cages, which, together with the complex atomic structure of W-S-N, is the key to ultra-low-friction in this functional material.

In the last chapter of the thesis a magnetic class of amorphous materials is addressed. Magnetic order in amorphous Gd-Fe ferrimagnet has been shown to undergo magnezation switching driven by a femtosecond laser pulse. Here, we combine first-principles density functional theory and atomistic spin dynamics simulations to explore this phenomena. A possible mechanism behind magnetization reversal in Gd-Fe based on a combination of the Dzyaloshinskii-Moriya interaction and exchange frustration is proposed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 105 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1276
Keyword [en]
first-principles theory, lattice dynamics, phase transitions, amorphous materials, tribology, ultrafast magnetism
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-260704ISBN: 978-91-554-9311-0 (print)OAI: oai:DiVA.org:uu-260704DiVA: diva2:848058
Public defence
2015-10-09, Å80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2015-09-16 Created: 2015-08-23 Last updated: 2015-10-01
List of papers
1. Lattice dynamics of cubic AuZn from first principles
Open this publication in new window or tab >>Lattice dynamics of cubic AuZn from first principles
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 10, 104101- p.Article in journal (Refereed) Published
Abstract [en]

We study the mechanism of the B2 -> R martensitic transformation in the shape memory alloy AuZn by means of first-principles theory. Phonon anomalies in the TA(2) acoustic branch along the Gamma-M [xi,xi,0] direction associated with a structural transformation are observed. The calculated Fermi surface of the B2 phase of AuZn reveals large portions nested with each other by a translation through a vector q = 1/3[1,1,0] associated with the soft mode. In addition, we find that the B2 phase can be stabilized by pressure in the low-temperature limit. The energetic barrier for the B2 -> R transition is 2 mRy and appears to be near a critical point.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-222732 (URN)10.1103/PhysRevB.89.104101 (DOI)000332453700003 ()
Available from: 2014-04-14 Created: 2014-04-14 Last updated: 2017-12-05Bibliographically approved
2. Understanding the phase transition in LiOsO3
Open this publication in new window or tab >>Understanding the phase transition in LiOsO3
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-260703 (URN)
Available from: 2015-08-23 Created: 2015-08-23 Last updated: 2015-10-01
3. Amorphous W-S-N thin films: The atomic structure behind ultra-low friction
Open this publication in new window or tab >>Amorphous W-S-N thin films: The atomic structure behind ultra-low friction
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2015 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 82, 84-93 p.Article in journal (Refereed) Published
National Category
Condensed Matter Physics Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-260693 (URN)10.1016/j.actamat.2014.08.043 (DOI)
Available from: 2015-08-23 Created: 2015-08-23 Last updated: 2017-12-04
4. All-thermal switching of amorphous Gd-Fe alloys: analysis of structural properties and magnetization dynamics
Open this publication in new window or tab >>All-thermal switching of amorphous Gd-Fe alloys: analysis of structural properties and magnetization dynamics
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(English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795Article in journal (Refereed) Submitted
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-260695 (URN)
Available from: 2015-08-23 Created: 2015-08-23 Last updated: 2017-12-04

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