NiAl 3 : a structure type of its own?

Abstract

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 geomet1ical and chemical pai{·}ameters 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 redetem1ined from single-crystal data: Pnma, a=6.613(1), b=7.367(1), c=4.81 l(l), Z=4. Compared to the pai{·}ent structure Fe3C, the coordination polyhedron for the min01ity 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.