Theoretical modelling of the defect structure of -phase alloys strongly supported experimental evidence which indicated that the presence of vacancies was responsible for a sharp decrease in the lattice parameter with increasing Al content in non-stoichiometric alloys. The results also hinted at the possibility that a more complex defect structure existed. This involved the presence of vacancies in the Ni and Al sub-lattices, and a preference for clustering or local ordering instead of a random distribution of point defects. Attention was also paid to the combining of first-principles results and semi-empirical methods for the simple and straightforward analysis of situations that could not be treated in a similar fashion by each technique individually. It was noted that the use of large computational cells for first-principles calculations would impose severe limitations upon the number and complexity of the configurations which could be considered. Also, the lack of suitable input data for a semi-empirical simulation technique would make it unreliable. The present results increased the degree of confidence which could be had in combining and applying these methods in the case of complex problems.

G.Bozzolo, C.Amador, J.Ferrante, R.D.Noebe: Scripta Metallurgica et Materialia, 1995, 33[12], 1907-13