The 2/1 cubic approximant of the Ag_(42)In_(42)Ca_(16) icosahedral quasicrystal

摘要

Using equal amounts of Ag and In to replace Cd in the stable Cd_(85)Ca_(15) icosahedral quasicrystal, Guo and Tsai obtained the stable Ag_(42)In_(42)Ca_(16) icosahedral quasicrystal. However, the crystalline approximant of this quasicrystal is still not known yet. In the present study, the simple cubic Ag_(42)In_(45)Ca_913) (Pa3-bar, a = 2.496 nm), displaying pseudo-icosahedral symmetry, has been found as the dominant phase in the ternary Ag_3In_3Ca alloy by electron and X-ray diffraction. Since the cubic Cd_6Ca (Im3-bar, a = 1.564nm) and Cd_(76)Ca_(13) (Pa3-bar, a = 2.5339nm), respectively, are known to be the 1/1 and 2/1 cubic approximants of the Cd_(85)Ca_(15) icosahedral quasicrystal, this cubic Ag_(42)In_(45)Ca_(13) may be considered the 2/1 approximant of the Ag_(42)In_(42)Ca_(16) icosahedral quasicrystal.