REFINEMENT OF THE FE4AL13 STRUCTURE AND ITS RELATIONSHIP TO THE QUASI-HOMOLOGICAL HOMEOTYPICAL STRUCTURES

The crystal structure of Fe4Al13 was refined using single crystal diff ractometer data: Pearson symbol mC102, space group C2/m; a = 15.492(2) angstrom, b = 8.078(2) angstrom, c = 12.471(1) angstrom, beta = 107.6 9(1)degrees; R(F) = 0.053, R(F)(w) = 0.044 for 1127 reflections and 13 7 refined parameters. The coordination numbers of atoms are 9, 10, 11 for iron and 10, 12, 13, 14 for aluminium. The shortest interatomic di stances are: Fe-Fe-2.902 angstrom, Fe-Al-2.374 angstrom, Al-Al-2.533 a ngstrom. A preferred occupation of pentagonal prismatic coordinated po sitions by aluminium was found. The structural relationship between th e Fe4Al13 structure and chemically homologous and homeotypical structu res of aluminium and gallium containing systems with the 3d transition metals is discussed. The greatest similarity was found concerning the coordination polyhedra, especially that of transition metal atoms. Th e main common feature of these homeotypical structures is the presence of pentagonal ''channels'', which is strongly dependent on the chemic al composition. With increasing atomic number of the 3d transition met al, the stability range of these structures shifts to the transition m etal-rich concentration. It is concluded that there is a connection be tween the occurrence of aluminium and gallium-containing decagonal and icosahedral phases and the existence of the infinite one-dimensional pentagonal channels in the intermetallic compounds showing a similar c hemical composition.