Synthesis and crystal structure determinations in the Γ and δ phase domains of the iron-zinc system:: Electronic and bonding analysis of Fe13Zn39 and FeZn10, a subtle deviation from the Hume-Rothery standard?

The iron-zinc system has been investigated in the zinc-rich domain. Alloying of Fe and Zn in ZnCl2 flux allowed the formation of well-developed single crystals of phases Fe13Zn39 and FeZn10 in a one-step experiment. These phases crystallize in cubic space group <I(4)over bar 3m> (Gamma) phase, Fe13Zn39, a = 8.994(2) Angstrom, Z = 1) and in the hexagonal space group P6(3)/mmc (delta phase, FeZn10, a = 12.787(3) Angstrom, c = 57.222(7), c/a = 4.475 Angstrom, Z similar to 50). The structure of Fe13Zn39 was reinvestigated and refined to R(F) of 3.28%; it is of the cubic Cu5Zn8 type. Its three-dimensional network is composed of fused tetrahedra of icosahedra (Fe/Zn) centered by Fe atoms. Fe/Zn occupational disorder has been accurately determined. The huge hexagonal structure of FeZn10 (c.a., Fe1.04(1)Zn10) has been determined for the first time and refined to R(F) of 6.84%. It contains 52 Fe and 504 Zn atoms and consists of a very dense packing of icosahedra and a few other polyhedra. Among the 52 independent atoms in the unit cell, seven atoms describe a disordered icosahedron spinning around a three-fold axis. Electronic properties are analyzed on the basis of tight-binding extended Huckel band calculations. The relationship of metallic bonding to clustering within the Fe13Zn39 phase has also been investigated using some electronic requirements for polyhedral condensation. (C) 2000 Academic Press.