Phase relations and structural properties of the ternary narrow gap semiconductors Zn5Sb4In2-δ (δ=0.15) and Zn9Sb6In2

A systematic study of the Zn-rich corner of the ternary system Zn-Sb-In revealed the presence of two ternary compounds: stable Zn5Sb4In2-δ (δ=0.15) and metastable Zn9Sb6In2 with closely related crystal structures. Their common motif is a tetragonal basic structure of 32434 nets formed by the Sb atoms. The nets are stacked in antiposition to yield layers of square antiprisms sharing edges plus intervening tetracapped tetrahedra (tetreadersterns). The majority of Zn atoms occupy peripheral tetrahedra of such tetraedersterns, which produces frameworks with a composition 'ZnSb'. These frameworks represent orthorhombic superstructures: (2x1x1) for Zn5Sb4In2-δ (Z=4) and (2x3x1) for Zn9Sb6In2 (Z=8) with respect to the tetragonal arrangement of Sb atoms. The In and remaining Zn atoms are distributed in the channels formed by the square antiprisms. Phase relations in the Zn-Sb-In system are complex. Crystals of metastable Zn9Sb6In2 are regularly intergrown with various amounts of Zn5Sb4In2-δ. Additionally, a monoclinic variant to orthorhombic Zn9Sb6In2 could be identified. Zn9Sb6In2 decomposes exothermically into a mixture of Zn5Sb4In2-δ, Zn4Sb3 and elemental Zn at around 480 K. Both Zn5Sb4In2-δ and Zn9Sb6In2 are poor metals with resistivity values that are characteristic of heavily doped or degenerate semiconductors (0.2-3 m Ω cm at room temperature). - Graphical abstract: A metastable intermetallic compound with the composition Zn9Sb6In2 has been identified in the ternary system Zn-Sb-In. Its structure relates to tetragonal CuAl2 in that it contains 32434 nets (formed by the Sb atoms) that are stacked in antiposition orientation.