Regensburg 2007 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 33: Diffusion and point defects II

MM 33.3: Talk

Thursday, March 29, 2007, 12:15–12:30, H6

Ab-initio modelling of defect properties in B2 NiAl — •Daniel Lerch, Kerrin Dössel, Stefan Müller, and Klaus Heinz — Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstr. 7, D-91058 Erlangen

The strongly ordering B2 phase of the intermetallic compound NiAl is known to be stable for a broad concentration range off its stoichiometry. Evidently this is due to the existence of constitutional defects. Experimental studies have shown that the dominant defect types in Al rich and Al poor parts of the B2 phase are Ni vacancies and Ni antisites (Ni atoms on the Al sublattice) respectively. We elucidate the ordering and ground state properties of defects in B2 NiAl on the basis of ab-initio calculations. We have applied the Cluster-Expansion (CE) formalism with Density Functional Theory (DFT) and the nudged elastic band method (as implemented within the computer code VASP) supplying the required input energies, as well as activation barriers for defect diffusion. Consistent with the existence of vacancies a full description of defects in NiAl bulk is only possible if vacancies are included by treating them as a third independent component within the CE formalism. One possible choice for a complete orthonormal basis set of point functions, required in such a ternary CE, are the first two Chebychev polynomials which were chosen in this case.

This work is supported by the "Studienstiftung des deutschen Volkes" which is gratefully acknowledged.