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Generation of Frenkel Defects above the Debye Temperature by Proliferation of Phonons near the Brillouin Zone Edge

Wednesday (26.09.2018)
11:45 - 12:00 S1/03 - 283
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Molecular Dynamics simulations show that Frenkel pairs of vacancies and interstitials in an aluminum single crystal can be induced by the proliferation of lattice vibrations near the Brillouin-Zone edge. The simulations were performed with periodic boundary conditions along the a- and b-axis of a single crystal, and with a free surface. An EAM potential for Al was employed. The lattice vibrations near Brillouin edge were injected at different rates. The vibrations were not correlated in phase. Surprisingly we find that Frenkel interstitials are created above the Debye temperature, but much below the melting point. The molar concentration of the Frenkel pairs was 10^–3 mol, which is far above equilibrium.

These results are consistent with flash experiments on polycrystals and single crystals of zirconium and titanium oxides where the Debye temperature was discovered to be the lower limit for the onset of the flash [1]. The presentation will attempt to draw a confluence between MD simulations and these experiments, even though the latter involve electrical fields while the simulations pertain only to the injection of lattice vibrations. The simulations may also be relevant to recent results on flash sintering of aluminum [2].

In summary, the present work suggests three conditions for the generation of Frenkel pairs: (i) sample temperature must be above the Debye threshold, (ii) lattice vibrations near the Brillouin Zone edge must be excited, and (iii) these vibrations must proliferate at a high rate.

Malte Jongmanns
University of Duisburg-Essen
Additional Authors:
  • Prof. Dr. Rishi Raj
    University of Colorado Boulder
  • Prof. Dr. Dietrich E. Wolf
    University of Duisburg-Essen