The study of the binary quasicrystal Cd₁₇Ca₃ and its 1/1 approximant Cd₆Ca by positron annihilation spectroscopy

Abstract

The positron annihilation lifetime measurements for the Cd₁₇Ca₃ quasicrystal and its 1/1 Cd₆Ca approximant were carried out at 300 K. The observed lifetime of the Cd₁₇Ca₃ quasicrystal is close to that of the 1/1 Cd₆Ca approximant, implying the existence of the same type of structural vacancies. The temperature variations in the positron lifetime were investigated in the temperature region from 10 to 300 K for the Cd₁₇Ca₃ quasicrystal annealed at 773 K and the Cd₁₇Ca₃ quasicrystal cooled in the furnace. We found clear differences between both the absolute value and the temperature gradient of the positron lifetimes of the two quasicrystals. The results will be discussed in terms of the fluctuation in the four-Cd tetrahedron inside the 20-Cd dodecahedron between two quasicrystals.