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Mechanical stability of TiO2 polymorphs under pressure: ab initio calculations
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: Journal of Physics: Condensed Matter, ISSN 0953-8984, Vol. 20, no 34, 345218- p.Article in journal (Refereed) Published
Abstract [en]

First-principles calculations using plane-wave basis sets and ultrasoft pseudopotentials have been performed to study the mechanical stabilities of the rutile, pyrite, fluorite and cotunnite phases of titanium dioxide (TiO2). For these polymorphs, we have calculated the equilibrium volumes, equations of state, bulk moduli and selected elastic constants. Compared to the three phases rutile, pyrite and fluorite, the recently discovered cotunnite phase shows the highest c44 for all pressures considered. Cotunnite also shows the highest bulk modulus amongst the four studied phases at an ambient pressure of B0 = 272 GPa.

Place, publisher, year, edition, pages
2008. Vol. 20, no 34, 345218- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97990DOI: 10.1088/0953-8984/20/34/345218ISI: 000258317600021OAI: oai:DiVA.org:uu-97990DiVA: diva2:173139
Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2009-10-08Bibliographically 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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