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Crystal structure of the pressure-induced metallic phase of SiH4 from ab initio theory
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
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2008 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 105, no 43, 16454-16459 p.Article in journal (Refereed) Published
Abstract [en]

Metallization of pure solid hydrogen is of great interest, not least because it could lead to high-temperature superconductivity, but it continues to be an elusive goal because of great experimental challenges. Hydrogen-rich materials, in particular, CH4, SiH4, and GeH4, provide an opportunity to study related phenomena at experimentally achievable pressures, and they too are expected to be high-temperature superconductors. Recently, the emergence of a metallic phase has been observed in silane for pressures just above 60 GPa. However, some uncertainty exists about the crystal structure of the discovered metallic phase. Here, we show by way of elimination, that a single structure that possesses all of the required characteristics of the experimentally observed metallic phase of silane from a pool of plausible candidates can be identified. Our density functional theory and GW calculations show that a structure with space group P4/nbm is metallic at pressures > 60 GPa. Based on phonon calculations, we furthermore demonstrate that the P4/nbm structure is dynamically stable at > 43 GPa and becomes the ground state at 97 GPa when zero-point energy contributions are considered. These findings could lead the way for further theoretical analysis of metallic phases of hydrogen-rich materials and stimulate experimental studies.

Place, publisher, year, edition, pages
2008. Vol. 105, no 43, 16454-16459 p.
Keyword [en]
hydrogen-rich, metallization
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97982DOI: 10.1073/pnas.0804148105ISI: 000260913500012OAI: oai:DiVA.org:uu-97982DiVA: diva2:173131
Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Ab initio Lattice Dynamics: Hydrogen-dense and Other Materials
Open this publication in new window or tab >>Ab initio Lattice Dynamics: Hydrogen-dense and Other Materials
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a theoretical study of materials under high pressure using ab initio lattice dynamics based on density functional theory and density functional perturbation theory using both super-cell and linear response approach.

Ab initio lattice dynamics using super-cell approach is applied to compare our theoretical predictions with experimental findings. Phonon dispersion curves of fcc α-γ cerium are calculated and compared with inelastic X-ray scattering data. Pressure dependency of phonon density of states in two cubic phases TiO2 allows us to assign the observed cubic phase in experiments to be of fluorite rather than pyrite structure. Dynamical stability of cotunnite TiO2 phase at low pressure can explain the observed quenching phenomena in experiments. Our calculated O2 vibron mode in both ε-ζ phases of solid oxygen supports the hypothesis that both phases are iso-structural.

Hydrogen-dense materials attract great attention not only because they open a path to study phenomena related to metallization (superconductivity) of solid hydrogen but also because they are closely related to important industrial applications (hydrogen storage). Using linear response method, we find that metallic fcc-AlH3 is dynamically stabilized in the range of 72-106 GPa and can persist at ambient pressure if finite temperature effects are considered. For SiH4, we test dynamical stability, Raman spectra, zero point energy, and utilize GW calculations for self energy correction. We find that a metallic tetragonal phase of SiH4 can be assigned to the experimentally observed one. Our ab initio lattice dynamics calculations based on density functional perturbation theory predict that fcc-YH3 is a pressure-induced superconductor with a high transition temperature of 40 K at 17.7 GPa. With increasing pressure this material undergoes a superconductor-metal-superconductor transition and the underlying mechanism of this transition can simultaneously explains also the observed metal-insulator transition at 25 GPa in YH3-δ.

Place, publisher, year, edition, pages
Uppsala: Universitetsbiblioteket, 2009. 80 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 597
Keyword
Density functional theory, Density functional perturbation theory, Hydrogen-dense materials, Phase transition, High pressure, Ab initio lattice dynamics, Superconductivity, Quasi-particle approximation
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-9535 (URN)978-91-554-7400-3 (ISBN)
Public defence
2009-02-26, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1 Uppsala, 10:15 (English)
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Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2010-03-08Bibliographically approved

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Scheicher, Ralph H.Ahuja, Rajeev

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