Crystal and electronic structures of TbCo0.29Li0.05Sn2 and TbCu0.25Li0.09Sn2

The new quaternary stannides, TbCo0.29Li0.05Sn2 and TbCu0.25Li0.09Sn2 crystallizes in the orthorhombic CeNiSi2 structure type with space group Cmcm. The four independent 4c atom positions (m2m site symmetry), three are fully occupied by individual atoms (two by Sn and one by Tb atoms) and the fourth is occupied by Li and transition metals Co or Cu atoms with a statistical distribution. The Tb coordination polyhedron is a 21-vertex pseudo-Frank–Kasper polyhedron. One Sn atom is enclosed in a tricapped trigonal prism, the second Sn atom is in a cuboctahedron and the statistically distributed (Li,Co or Cu) site is in a tetragonal antiprism with one added atom. Electronic structure calculations were used for the elucidation of reasons for and the ability of mutual substitution of lithium and transition metals. Positive charge density was observed around the rare earth atom and the Li and transition metal atoms, the negative charge density in the proximity of the Sn atoms.