Über hexagonale Perowskite mit Kationenfehlstellen. XII. Strukturbestimmung an Ba6W4□2O18

On Hexagonal Perovskites with Cationic Vacancies. XII. Structure Determination on Ba₆W₄□₂O₁₈ The stacking polytype Ba₆W₄□₂O₁₈ is the first oxidic variant of the Cs₃Tl₂Cl₉-type. The structure determination gave for the space group R3 c with the sequence (h)₆, Z = 3, the refined, intensity related R′ value of 6.8%. The octahedral net consists of groups of two face sharing WO₆ octahedra (W₂O_6/2;O₆), which are in the (110) plane displaced against each other. In the doublé octahedra the tungsten atoms are shifted away from their ideal central position (W–W: 2.32₇ Å) with the result, that the W–W distance has increased to 2.90₅ Å.