The Sodium Antimony Telluridogermanate(III) Na 9 Sb[Ge 2 Te 6 ] 2

Systematic studies in the quaternary system Na/Ge/Sb/Te yielded the new compound Na 9 Sb[Ge 2 Te 6 ] 2 . Its crystal structure is isotypic to Na 9 Sb[Ge 2 Se 6 ] 2 (space group C 2/ 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 [Ge 2 Te 6 ] 6– anions. Cation sites are occupied by Na + as well as shared by Na + and Sb 3+ . Na 9 Sb[Ge 2 Te 6 ] 2 is formally obtained from the reaction of one equivalent Na 8 [Ge 4 Te 10 ] and one equivalent NaSbTe 2 . In contrast to members of the metastable solid solution series (NaSbTe 2 ) 1– x (GeTe) x , Na 9 Sb[Ge 2 Te 6 ] 2 is a thermodynamically stable compound. It is a semiconductor with a bandgap of 1.51 eV.