Structure, bonding, and properties of CaZn_1−xCd_xSn and CaSn_0.5Ge_1.5

Abstract

CaZnSn, the end member of the CaZn_1−xCd_xSn series, crystallizes in the LiGaGe structure type, an ordered ternary version of Caln₂ (space group P6₃mc, Z = 2, a = 4.621(2) Å, c = 7.643(2) Å). Alternating Zn and Sn form puckered hexagonal layers that are interconnected by 0.40 Å, longer Zn-Sn bonds (around intercalated Ca) to form a distorted wurtzite-like framework. This structure is retained through x = 0.75. The other member, CaCdSn, has the Fe₂P structure type (space group P6¯ 2m, Z = 4, a = 7.6319(5), c = 4.6996(4) Å) and consists of two kinds of augmented trigonal prisms of Ca and Cd centered by different Sn atoms. CaSn_0.52(2)Ge1.48(2) crystallizes in the P6₃mc space group (a = 4.117(1), c = 10.300 (3) Å) and has the KSnAs structure, with puckered ordered layers of Sn and Ge separated by calcium. The composition is the tin-rich limit of stability. The CaZn_1−xCd_xSn phases for x = 0, 0.25, 0.50 are weak Pauli paramagnets and poor metals (~50 μΩ·cm at 290 K). Distortions of the hexagonal wurtzite-based matrix by the inserted Ca are thought to be responsible for this unexpected result. CaCdSn and CaSn_0.5Ge_1.5 are diamagnetic although the former shows a nearly temperature-independent resistivity of ~35 μΩ·cm.