Copper and Zinc Substitutions in Clathrates of Tin: Synthesis, Structural Characterization, and Physical Properties of A8Cu2.67Sn43.33 and A8Zn4Sn42 (A = K, Rb, Cs) with the Type-I Structure

Reported are two series of tin-based clathrates—A8Cu2.67Sn43.33 and A8Zn4Sn42 (A = K, Rb, Cs)—crystallizing in the cubic type-I structure. The six new compounds have been obtained in quantitative yields and have been characterized by single-crystal X-ray diffraction. Copper and zinc randomly substitute tin on only one of the three framework sites, 6c, while the remaining two sites 16i and 24k are exclusively occupied by tin. The alkali metals reside in the two types of cages in the structure—the 20-atom dodecahedra and the 24-atom tetrakaidecahedra. According to the structure refinements, both cages are completely filled; in the bigger tetrakaidecahedron, the smaller K and Rb atoms are displaced off its center, whereas the larger Cs atoms are located at the center. These findings are presented and discussed; preliminary results from measurements of the Seebeck coefficients (300–500 K) and the electrical resistivity (100–400 K) are presented as well.