NiAl₃: A STRUCTURE TYPE OF ITS OWN? Per Viklund, Ulrich Häußermann, Sven Lidin, Inorganic Chemistry 2, University of Lund, S-221 00 Lund, Sweden

Generally, the intermetallic compound NiAl₃ is counted as a representative of the Fe₃C (cementite) structure type. We grouped the almost 200 different compounds with the cementite structure type according to geometrical and chemical parameters and found that NiAl₃ is not fitting the values typical of this structure type.

NiAl₃ was prepared by slowly annealing an Al-rich melt and dissolving excess Al in dilute hydrochloric acid. The crystal structure was redetermined from single-crystal data: Pnma, a=6.613(1), b=7.367(1), c=4.811(1), Z=4.

Compared to the parent structure Fe₃C, the coordination polyhedron for the minority component changes from a trigonal prism with nearly equal edges to a distorted prism with all quadrilateral faces capped.

We suggest that NiAl₃ is better described by a structure type of its own rather than by the cementite structure.