Li 9 Al 4 Sn 5 as a new ordered superstructure of the Li 13 Sn 5 type.

Alloys from the ternary Li-Al-Sn system have been investigated with respect to possible applications as negative electrode materials in Li-ion batteries. This led to the discovery of a new ternary compound, a superstructure of the Li13 Sn5 binary compound. The ternary stannide, Li9 Al4 Sn5 (nonalithium tetraaluminium pentastannide; trigonal, P-3m1, hP18), crystallizes as a new structure type, which is an ordered variant of the binary Li13 Sn5 structure type. One Li and one Sn site have -3m. symmetry, and all other atoms occupy sites of 3m. symmetry. The polyhedra around all types of atoms are rhombic dodecahedra. The electronic structure was calculated by the tight-binding linear muffin-tin orbital atomic spheres approximation method. The electron concentration is higher around the Sn and Al atoms, which form an [Al4 Sn5 ]m- polyanion.