K₇In₄As₆ and K₃InAs₂ - Two more Zintl phases showing the rich variety of In-As polyanion structures

Binary phases of triel (Tr) and pentel (Pn) elements (III-V semiconductors) represent a unique compound class due to their tunable intrinsic band gap in dependency of the element combination. We report here on two new compounds in the ternary system K−In−As. In K₃InAs₂ the edge-sharing tetrahedral InAs₄ units are connected via opposed edges of the tetrahedra forming linear [InAs₂]³⁻ chains and are thus iso(valence)- electronic with SiS₂. In K₇In₄As₆, the InAs₄ tetrahedra are connected via neighboring edges of the tetrahedra forming zig-zag chains. These chains are linked in two directions through dimeric [As₃In−InAs₃] units. Both reported Zintl phases extend the number of structures that possess the same In−As ratio. In K₃InAs₂ a one-dimensional polyanion in contrast to known Na₃InAs₂ comprising a three-dimensional polyanion structure is found. K₇In₄As₆ forms together with the known phases K₂In₂As₃ and K₃In₂As₃ a series of Zintl phases with the ratio In : As=2 : 3. Even though the three phases differ only slightly in their valence electron concentration (VEC) of the polyanion, the VECs have a strong influence on the structures. Syntheses, crystal structures and the electronic band structures are reported. The compounds are discussed in the context of the Zintl concept.