Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
MM: Metall- und Materialphysik
MM 22: Electronic Properties II
MM 22.4: Vortrag
Mittwoch, 29. März 2006, 14:45–15:00, IFW A
The intrinsic defect structure of Al1−xB2 – an ab initio electronic structure study — •Katrin Koch, Yuri Grin, and Helge Rosner — MPI CPfS Dresden
Ab initio calculation of phase diagrams is still in its very early stages.
For an outset towards new developments, we have chosen the simple hexagonal system AlB2,
which is nevertheless very interesting due to its close relation to the surprising
superconductor MgB2.
Up to now, the synthesis of stoichiometric AlB2 has been impossible:
grown in aluminium flux, a composition between Al0.9B2 (from x-ray refinement)
and Al0.85B2 (from mass density measurements) has been found [1].
Here, we present band structure calculations within the local density approximation
to investigate the structural stability in the phase equilibrium
AlB2 ⇐⇒ Al1−xB2 + x·Al.
The defects are treated using the coherent potential approximation (CPA). Taking
into account the full lattice relaxation depending on x, we find a stable energy
minimum for the composition Al0.85B2.
This is in excellent agreement with the experimental findings and explains the
nonstoichiometric composition of present AlB2 samples.
The influence of the defects on the electronic properties will be discussed.
[1] U.Burkhardt et al. Journal of Solid State Chemistry 177, 389, (2004)