F-TYPE ICOSAHEDRAL PHASE AND A RELATED CUBIC PHASE IN THE AL-RH-CU SYSTEM

An F-type icosahedral phase and a related cubic phase (composition of Al66.1Rh21.5Cu12.3, lattice constant a = 1.5380(2) nm, and space group of Fm3) were observed in the Al63Rh18.5Cu18.5 alloy by transmission e lectron microscopy (TEM). The structure of the Al-Rh-Cu cubic phase wa s determined by single-crystal X-ray analysis. A high-resolution elect ron microscopic image of the Al-Rh-Cu cubic phase is presented togethe r with a simulated image. The structure of the cubic phase can be desc ribed by two types of atom clusters, which have outer shells with icos ahedral symmetry. It is suggested that the structure of the Al-Rh-Cu c ubic phase is helpful for understanding the structure of the i-Al-Rh-C u F-type icosahedral quasicrystal.