Phase relations and structural properties of the ternary narrow gap semiconductors Zn₅Sb₄In_2-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 Zn₅Sb₄In_2-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: (2×1×1) for Zn₅Sb₄In_2-δ (Z=4) and (2×3×1) 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 Zn₅Sb₄In_2-δ. Additionally, a monoclinic variant to orthorhombic Zn₉Sb₆In₂ could be identified. Zn₉Sb₆In₂ decomposes exothermically into a mixture of Zn₅Sb₄In_2-δ, Zn₄Sb₃ and elemental Zn at around 480 K. Both Zn₅Sb₄In_2-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).