Semiconducting Ba3Sn3Sb4 and Metallic Ba7-xSn11Sb15-y (x = 0.4, y = 0.6) Zintl Phases.

We report the discovery of two ternary Zintl phases Ba3Sn3Sb4 and Ba7-xSn11Sb15-y (x = 0.4, y = 0.6). Ba3Sn3Sb4 adopts the monoclinic space group P21/c with a = 14.669(3) Å, b = 6.9649(14) Å, c = 13.629(3) Å, and β = 104.98(3)°. It features a unique corrugated two-dimensional (2D) structure consisting of [Sn3Sb4]6- layers extending along the ab-plane with Ba2+ atoms sandwiched between them. The nonstoichiometric Ba6.6Sn11Sb14.4 has a complex one-dimensional (1D) structure adopting the orthorhombic space group Pnma, with unit cell parameters a = 37.964(8) Å, b = 4.4090(9) Å, and c = 24.682(5) Å. It consists of large double Sn-Sb ribbons separated by Ba2+ atoms. Ba3Sn3Sb4 is an n-type semiconductor which has a narrow energy gap of ∼0.18 eV and a room temperature carrier concentration of ∼4.2 × 1018 cm-3. Ba6.6Sn11Sb14.4 is determined to be a metal with electrons being the dominant carriers.