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Anomalous Thermal Expansion in α-Titanium
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
2007 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 1, 015901- p.Article in journal (Refereed) Published
Abstract [en]

We provide a complete quantitative explanation for the anisotropic thermal expansion of hcp Ti at low temperature. The observed negative thermal expansion along the c axis is reproduced theoretically by means of a parameter free theory which involves both the electron and phonon contributions to the free energy. The thermal expansion of titanium is calculated and found to be negative along the c axis for temperatures below ∼170 K, in good agreement with observations. We have identified a saddle point van Hove singularity near the Fermi level as the main reason for the anisotropic thermal expansion in α-titanium.

Place, publisher, year, edition, pages
2007. Vol. 99, no 1, 015901- p.
Keyword [en]
Thermal expansion; thermomechanical effects, Phonon states and bands, normal modes, and phonon dispersion, Transition metals and alloys
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96176DOI: 10.1103/PhysRevLett.99.015901ISI: 000247819900024OAI: oai:DiVA.org:uu-96176DiVA: diva2:170662
Available from: 2007-09-13 Created: 2007-09-13 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Electronic Structure and Lattice Dynamics of Elements and Compounds
Open this publication in new window or tab >>Electronic Structure and Lattice Dynamics of Elements and Compounds
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The elastic constants of Mg(1-x)AlxB2 have been calculated in the regime 0<x<0.25. The calculations show that the ratio, B/G, between the bulk- and the shear-modulus stays well below the empirical ductility limit, 1.75, for all concentrations, indicating that the introduction of Al will not change the brittle behaviour of the material considerably. Furthermore, the tetragonal elastic constant C’ has been calculated for the transition metal alloys Fe-Co, Mo-Tc and W-Re, showing that if a suitable tuning of the alloying is made, these materials have a vanishingly low C'. Thermal expansion calculations of the 4d transition metals have also been performed, showing good agreement with experiment with the exception of Nb and Mo. The calculated phonon dispersions of the 4d metals all give reasonable agreement with experiment. First principles calculations of the thermal expansion of hcp Ti have been performed, showing that this element has a negative thermal expansion along the c-axis which is linked to the closeness of the Fermi level to an electronic topological transition. Calculations of the EOS of fcc Au give support to the suggestion that the ruby pressure scale might underestimate pressures with ~10 GPa at pressures ~150 GPa. The high temperature bcc phase of the group IV metals has been calculated with the novel self-consistent ab-initio dynamical (SCAILD) method. The results show good agreement with experiment, and the free energy resolution of < 1 meV suggests that this method might be suitable for calculating free energy differences between different crystallographic phases as a function of temperature.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 127 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 338
Keyword
Atomic and molecular physics, electronic structure, lattice dynamics, first-principles theory, self-consistent lattice dynamical calculation, elasticity, super plasticity, electronic topological transition, equation of state, Atom- och molekylfysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-8198 (URN)978-91-554-6960-3 (ISBN)
Public defence
2007-10-05, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Box 530, Uppsala University, SE-75121, Uppsala, 10:15
Opponent
Supervisors
Available from: 2007-09-13 Created: 2007-09-13 Last updated: 2012-04-01Bibliographically approved

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Souvatzis, PetrosEriksson, Olle

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