Chemical speciation in Gd−Cd−M (M=Zn, Au) quasicrystal approximants

Abstract

We investigated the effect of partial replacement of Cd by M=Au and Zn in the crystal structure of the 1/1 Tsai-type quasicrystal approximant (AC) GdCd6. Compositionally homogeneous single crystal samples Gd(Cd0.87Zn0.13(1))6 and Gd(Cd0.80Au0.20(1))6 were grown from melts Gd5(Cd0.8Zn0.2)100 and Gd1(Cd0.9Au0.1)100, respectively, and isolated by centrifugation. The M for Cd substitution in GdCd6 is accompanied with a sizeable reduction of the cubic unit cell parameter, from 15.514(2) Å to 15.329(1) Å (Zn) and 15.314(1) Å (Au). Site preferences were established from single crystal X-ray diffraction data. A clear preference of atomic sites for Au and Zn is noted which is compared to earlier reported Yb(Cd0.75Mg0.25)6. Three and two out of in total seven crystallographic sites defining the Cd partial structure accept preferably metals more and less electronegative than Cd, respectively, and are classified as negatively and positively polarized sites in the binary 1/1 AC.