The 2/1 cubic approximant of the Ag42In42Ca16 icosahedral quasicrystal

Using equal amounts of Ag and In to replace Cd in the stable Cd85Ca15 icosahedral quasicrystal, Guo and Tsai obtained the stable Ag42In42Ca16 icosahedral quasicrystal. However, the crystalline approximant of this quasicrystal is still not known yet. In the present study, the simple cubic Ag42In45Ca13 (Pa (3) over bar, a = 2.496 nm), displaying pseudo-icosahedral symmetry, has been found as the dominant phase in the ternary Ag3In3Ca alloy by electron and X-ray diffraction. Since the cubic Cd6Ca (Im (3) over bar, a = 1.564 nm) and Cd76Ca13 (Pa (3) over bar, a = 2.5339 nm), respectively, are known to be the 1/1 and 2/1 cubic approximants of the Cd85Ca15 icosahedral quasicrystal, this cubic Ag42In45Ca13 may be considered the 2/1 approximant of the Ag42In42Ca16 icosahedral quasicrystal. (C) 2003 Elsevier B.V. All rights reserved.