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Structural and Vibrational Properties of Layered Data Storage Material: Ge2Sb2Te5
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
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2013 (English)In: SCI ADV MATER, ISSN 1947-2935, Vol. 5, no 10, 1493-1497 p.Article in journal (Refereed) Published
Abstract [en]

Ge2Sb2Te5 is a prototype material for phase-change memory, while its stable layered phase was recently predicted to be a topological insulator. In this work, we show that standard density functional theory (DFT) calculations provide much larger Te-Te bond length and lattice parameters for layered Ge2Sb2Te5 compared with experimental results. However, by considering van der Waals interactions in DFT calculations, we obtained correct structure information and lattice dynamics properties. It is clear that the discrepancy results from the neglecting the van der Waals interaction between directly weak bonded adjacent Te atoms.

Place, publisher, year, edition, pages
2013. Vol. 5, no 10, 1493-1497 p.
Keyword [en]
Chalcogenide, Density Functional Theory Calculations, Weak Bond, Layered Structure
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-208353DOI: 10.1166/sam.2013.1610ISI: 000323356200021OAI: oai:DiVA.org:uu-208353DiVA: diva2:652600
Available from: 2013-10-01 Created: 2013-09-30 Last updated: 2015-05-12Bibliographically approved
In thesis
1. First-Principles Studies of Materials Properties: Pressure-Induced Phase Transitions & Functional Materials
Open this publication in new window or tab >>First-Principles Studies of Materials Properties: Pressure-Induced Phase Transitions & Functional Materials
2015 (English)Doctoral thesis, comprehensive summary (Other academic) [Artistic work]
Abstract [en]

This thesis presents the first-principles studies of materials properties within the framework of the density functional theory (DFT). The thesis constitutes three main parts, i. e., pressure-induced phase transitions in solids, data-storage and clean-energy materials.

The first part focuses on the predictions of crystal structures and the determinations of electronic properties of Xe-H2, FeB4 and Co3O4. Pressurizing Xe-H2 compound yields the formation of H-rich Xe(H2)8, which can exhibit a metallic feature at comparatively lower pressure than pure hydrogen. Hard superconducting FeB4 gets transformed into a novel transparent phase under pressure owing to the enhanced overlap of atomic cores. Spinel Co3O4 undergoes the phase transition from a cubic to a monoclinic because of the charge transfer between cations via the increased 3d-3d interactions.

The second part involves the study of structural and electronic properties of phase-change memory materials (PCMs), i. e., Ge2Sb2Te5 (GST) and Ga-doped In2O3. Van der Waals (vdW) interaction must be considered to obtain accurate crystal structure of layered GST. For Ga-doped In2O3 (GIO), the local structure of amorphous GIO is found to resemble that of amorphous In2O3, except the vicinity of doping atoms. The electronic property of a-GIO is metallic, which considerably differs from the semiconducting feature of the crystalline GIO. This emphasizes the contrast in the conductivity of the crystalline and amorphous upon phase switching of GIO.

The third part associates with the search for clean-energy materials, viz., hydrogen production, hydrogen storage and green Mg-ion batteries. For hydrogen production, the role of intrinsic point defects to water adsorption on ZnO(10-10) surface is investigated. The findings show that the Zn and O defect-sites are energetically not favorable for the water adsorption and dissociation. For the purpose of storing hydrogen in a solid phase, silicene, doped by alkaline and alkaline earth metals, is investigated. We find that Li-doped and Na-doped silicene can attain the superior storage capacity. For cathode material of Mg-ion batteries, Mg2Mo6S8, the diffusivity of Mg ions occurs through an available channel in the bulk with the onset temperature of 200 K.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 69 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1254
Density functional theory, Pressure-induced phase transitions, Ab-initio molecular dynamic, hybrid functional, Ab-initio random structure searching, Phase change material
National Category
Physical Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
urn:nbn:se:uu:diva-251343 (URN)978-91-554-9247-2 (ISBN)
Public defence
2015-06-05, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Available from: 2015-05-12 Created: 2015-04-15 Last updated: 2015-07-07

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Kaewmaraya, ThanayutAhuja, Rajeev
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