The Al3Ni2 Structure as Approximant of Quasicrystals

The present paper discusses the approximant nature of the A13N12 structure from the viewpoint of valence electron concentration (VEC) correspondence as well as from atomic structure correlation. Its VEC is close to that of corresponding quasicrystals and its atomic structure can be descnbed by layers stacked along the direction corresponding to the 10-fold axis of the decagonal phase. A large orthorhombic pseudocell is proposed whose edges are integer multiplication of those of a basic Cscl unit along directions corresponding to the orthogonal 10fold and two 2-fold axes of the decagonal phase. Thus its structure con be expressed in the form of A13N12-(1,3,3) or A13N12-(3,1,3), the integers being the multiphcity of the Cscl unit along the three directions. The generalization of this expression to several other approximants mdicates that approximants can be related to each other by packing the basic Cscl pseudocells