A single-crystal study of barium tungsten lithium oxide: a compound with a ten-layer structure

A single-crystal study of a sample of barium tungsten lithium oxide, supplied by Dr. T. Negas and identified as Ba₅W₃Li₂O₁₅, confirms the |(5)|(5)| layer stacking scheme (Zhdanov notation) for the ten BaO₃ layers per unit cell. Pairs of face-sharing MO₆ octahedra (MW or Li) are linked through corner sharing by strings of three corner-sharing octahedra. In these strings of three, the two outer octahedra are occupied by W; but no X-ray evidence was found for the existence of Li in the middle one. The compound has an hexagonal cell of dimensions a = 5.7614 ± 0.0008 Å and c = 23.719 ± 0.007 Å, probable space group $\text{P6}{}_3\text{mmc}\text{, Z = 2}$. Its structure was determined from 757 independent reflections, of which 426 were considered observed, collected by automated counter methods, and refined by least-squares methods to a conventional R of 0.064. The X-ray refinement based on the assumption that two octahedral sites in the unit cell are empty suggests formulas such as Ba₅W_3.2Li_0.8O₁₅ or Ba₅W₃LiO_14.5 rather than the “ideal” formula Ba₅W₃Li₂O₁₅.