Refinement of the Fe₄Al₁₃ structure and its relationship to the quasihomological homeotypical structures

The crystal structure of Fe₄Al₁₃ was refined using single crystal diffractometer data: Pearson symbol mC102, space group C2/m; a = 15.492(2) Å, b = 8.078(2) Å, c = 12.471(1) Å, β = 107.69(1)°; R_F = 0.053, R_F (w) = 0.044 for 1127 reflections and 137 refined parameters. The coordination numbers of atoms are 9, 10. 11 for iron and 10, 12, 13, 14 for aluminium. The shortest interatomic distances are: Fe–Fe – 2.902 Å, Fe–Al – 2.374 Å, Al–Al – 2.533 Å. A preferred occupation of pentagonal prismatic coordinated positions by aluminium was found. The structural relationship between the Fe₄Al₁₃ structure and chemically homologous and homeotypical structures 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. The main common feature of these homeotypical structures is the presence of pentagonal “channels”, which is strongly dependent on the chemical composition. With increasing atomic number of the 3d transition metal, the stability range of these structures shifts to the transition metal-rich concentration. It is concluded that there is a connection between 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 chemical composition.