Si Extraction from Silica in a Basic Polychalcogenide Flux. Stabilization of Ba₄SiSb₂Se₁₁, a Novel Mixed Selenosilicate/Selenoantimonate with a Polar Structure

Abstract

An unusual compound, Ba4SiSb2Se11, was discovered from a reaction of Ba/Th/Sb/Se. It is assumed that Si was extracted from the silica reaction tube. It forms as silver needlelike crystals in the polar space group Cmc21 with a = 9.3981(3) Å, b = 25.7192(7) Å, c = 8.7748 (3) Å, and Z = 4. A rational synthesis has been devised at 600 °C. The compound is composed of Ba2+ ions stabilized between infinite one-dimensional [SiSb2Se11]8- chains running parallel to the a axis. Each chain is composed of a [SbSe2]-∞ backbone with [SiSe4]4- tetrahedra chelating every other Sb atom from the same side of the backbone. The V-shaped triselenide groups, (Se3)2-, are attached to the rest of the Sb atoms in the chain through one of their terminal Se atoms. The compound has a band gap of 1.43 eV. The Raman spectrum shows a broad shift at 247 cm-1 and a shoulder around 234 cm-1, which are related to the Se−Se vibration of the triselenide groups and/or the Si−Se vibrations of the [SiSe4]4- groups. The compound decomposes at 522 °C