Regensburg 2016 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 30: Structural Materials I
MM 30.1: Vortrag
Mittwoch, 9. März 2016, 10:15–10:30, H52
Thermodynamic properties of ultra-high temperature ceramics: ab initio accuracy up to the melting point — •Andrew Duff1, Dominique Korbmacher2, Albert Glensk2, Blazej Grabowski2, Joerg Neugebauer2, and Michael Finnis1 — 1Department of Materials, Thomas Young Centre, Imperial College London, Exhibition Road, London SW7 2AZ, UK — 2Max-Planck-Institut für Eisenforschung, Max-Planck-Strasse 1, Düsseldorf 40237, Germany
A new method for calculating ab initio thermodynamic properties of materials is presented. The new approach, termed TU-TILD (two-stage upsampled thermodynamic integration using Langevin dynamics) captures the full anharmonicity of the lattice vibrations and provides at least an order of magnitude improvement in efficiency compared to the UP-TILD approach on which it is based. Using TU-TILD, free energies can be calculated up to the melting point at the full accuracy of the underlying ab initio theory-- in the present case, density functional theory --overcoming limitations of the widely used quasiharmonic approximation, whilst significantly closing the gap in computational efficiency between fully anharmonic and quasiharmonic methodologies. The new approach is used to calculate thermodynamic properties of the ultra-high temperature ceramics: zirconium carbide; zirconium diboride and hafnium carbide. The results show a distinct improvement over quasiharmonic calculations, with heat capacities and thermal expansion data brought more closely in line with experimental results and, where available, the results of CALPHAD assessments.