Syntheses, crystal structures, and electronic properties of Ba₈Si₂US₁₄ and Ba₈SiFeUS₁₄

Abstract Black single crystals of the new compounds Ba₈Si₂US₁₄ and Ba₈SiFeUS₁₄ have been obtained by high-temperature solid-state methods at 1223 K. These isostructural compounds crystallize in a new structure type in space group C2h3 - C2/m of the monoclinic system. The salt-like structure comprises isolated US₆ octahedra and MS₄ tetrahedra separated by Ba cations. The US₆ octahedra form pseudo-layers that are separated by two other pseudo-layers formed by isolated MS₄ tetrahedra. These compounds do not show any short S-S interactions. Ba₈Si₂US₁₄ charge balances with 8 Ba²⁺, 2 Si⁴⁺, 1 U⁴⁺, and 14 S^2-; Ba₈SiFeUS₁₄ can be charge balanced with 8 Ba²⁺, 1 Si⁴⁺, 1 Fe³⁺, 1 U⁵⁺, and 14 S^2-. DFT calculations using the HSE functional indicate that the compounds are semiconductors. The calculated band gaps are 1.2 eV and 1.8 eV for Ba₈Si₂US₁₄ and Ba₈SiFeUS₁₄, respectively.