The Sodium Antimony Telluridogermanate(III) Na9Sb[Ge2Te6]2

Systematic studies in the quaternary system Na/Ge/Sb/Te yielded the new compound Na₉SbGe₂Te₆]₂. Its crystal structure is isotypic to Na₉SbGe₂Se₆]₂ (space group C2/c with a = 9.541(2), b = 26.253(7), c = 7.5820(18) Å and β = 122.233(15)°, Z = 2). The structure is characterized by Ge–Ge dumbbells that are octahedrally coordinated by Te, forming ethane‐like Ge₂Te₆]^6– anions. Cation sites are occupied by Na⁺ as well as shared by Na⁺ and Sb³⁺. Na₉SbGe₂Te₆]₂ is formally obtained from the reaction of one equivalent Na₈Ge₄Te₁₀] and one equivalent NaSbTe₂. In contrast to members of the metastable solid solution series (NaSbTe₂)_1–x(GeTe)_x, Na₉SbGe₂Te₆]₂ is a thermodynamically stable compound. It is a semiconductor with a bandgap of 1.51 eV.