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Local structure of liquid Ge1Sb2Te4 for rewritable data storage use
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
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2008 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 20, 205102- p.Article in journal (Refereed) Published
Abstract [en]

Phase-change materials based on chalcogenide alloys have been widely used for optical data storage and are promising materials for nonvolatile electrical memory use. However, the mechanism behind the utilization is unclear as yet. Since the rewritable data storage involved an extremely fast laser melt-quenched process for chalcogenide alloys, the liquid structure of which is one key to investigating the mechanism of the fast reversible phase transition and hence rewritable data storage, here by means of ab initio molecular dynamics we have studied the local structure of liquid Ge1Sb2Te4. The results show that the liquid structure gives a picture of most Sb atoms being octahedrally coordinated, and the coexistence of tetrahedral and fivefold coordination at octahedral sites for Ge atoms, while Te atoms are essentially fourfold and threefold coordinated at octahedral sites, as characterized by partial pair correlation functions and bond angle distributions. The local structure of liquid Ge1Sb2Te4 generally resembles that of the crystalline form, except for the much lower coordination number. It may be this unique liquid structure that results in the fast and reversible phase transition between crystalline and amorphous states.

Place, publisher, year, edition, pages
2008. Vol. 20, no 20, 205102- p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-130227DOI: 10.1088/0953-8984/20/20/205102ISI: 000255661500057OAI: oai:DiVA.org:uu-130227DiVA: diva2:348766
Conference Information: 11th International Conference on Magnetic Fluids Kosice, SLOVAKIA, JUL 23-27, 2007 Available from: 2010-09-04 Created: 2010-09-04 Last updated: 2012-03-05Bibliographically approved
In thesis
1. Insights into Materials Properties from Ab Initio Theory: Diffusion, Adsorption, Catalysis & Structure
Open this publication in new window or tab >>Insights into Materials Properties from Ab Initio Theory: Diffusion, Adsorption, Catalysis & Structure
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, density functional theory (DFT) calculations and DFT based ab initio molecular dynamics simulations have been employed in order to gain insights into materials properties like diffusion, adsorption, catalysis, and structure.

In transition metals, absorbed hydrogen atoms self-trap due to localization of metal d-electrons. The self-trapping state is shown to highly influence hydrogen diffusion in the classical over-barrier jump temperature region. Li diffusion in Li-N-H systems is investigated. The diffusion in Li3N is shown to be controlled by the concentration of vacancies. Exchanging one Li for H (Li2NH), gives a system where the diffusion no longer is dependent on the concentrations of vacancies, but instead on N-H rotations. Furthermore, exchanging another Li for H (LiNH2), results in a blockade of Li diffusion. For high-surface area hydrogen storage materials, metal organic frameworks and covalent organic frameworks, the hydrogen adsorption is studied. In metal organic frameworks, a Li-decoration is also suggested as a way to increase the hydrogen adsorption energy. In NaAlH4 doped with transition metals (TM), the hypothesis of TM-Al intermetallic alloys as the main catalytic species is supported. The source of the catalytic effect of carbon nanostructures on hydrogen desorption from NaAlH4 is shown to be the high electronegativity of the carbon nanostructures. A space-group optimized ab initio random structure search method is used to find a new ground state structure for BeC2 and MgC2. The fast change between the amorphous and the crystalline phase of GeSbTe phase-change materials is suggested to be due to the close resemblance between the local amorphous structure and the crystalline structure. Finally, we show that more than 80% of the voltage in the lead acid battery is due to relativistic effects.


Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 81 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 772
Density functional theory, Molecular dynamics, Diffusion, Catalysis, Adsorption, Random structure search, Hydrogen-storage materials, Phase-change materials
National Category
Condensed Matter Physics Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
urn:nbn:se:uu:diva-131331 (URN)978-91-554-7907-7 (ISBN)
Public defence
2010-11-12, Siegbansalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 702Available from: 2010-10-21 Created: 2010-09-30 Last updated: 2011-04-04Bibliographically approved

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