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Formation of Large Voids in the Amorphous Phase-Change Memory Ge2Sb2Te5 Alloy
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
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2009 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 7, 075504- p.Article in journal (Refereed) Published
Abstract [en]

Onthe basis of ab initio molecular dynamics simulations, large voids mainlysurrounded by Te atoms are observed in molten and amorphousGe2Sb2Te5, which is due to the clustering of two- andthreefold coordinated Te atoms. Furthermore, pressure shows a significant effecton the clustering of the under coordinated Te atoms andhence the formation of large voids. The present results demonstratethat both vacancies and Te play an important role inthe fast reversible phase transition process.

Place, publisher, year, edition, pages
2009. Vol. 102, no 7, 075504- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-100532DOI: 10.1103/PhysRevLett.102.075504ISI: 000263599500040PubMedID: 19257687OAI: oai:DiVA.org:uu-100532DiVA: diva2:210453
Available from: 2009-04-01 Created: 2009-04-01 Last updated: 2017-12-13Bibliographically 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.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 772
Keyword
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
Identifiers
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)
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Note
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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Johansson, BörjeAhuja, Rajeev

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