Double-Icosahedral Li Clusters in a New Binary Compound Ba19Li44:  A Reinvestigation of the Ba−Li Phase Diagram

The binary Ba−Li system was reinvestigated for compositions with less than 80 at. % Li. A new compound, Ba19Li44, stable up to 126 °C, was found and structurally characterized. According to single-crystal X-ray diffraction data, the compound crystallizes in a new structure type with a tetragonal unit cell, space group I4̄2d, a = 16.3911(5) Å, c = 32.712(1) Å, Z = 4, and V = 8788.7(5) Å3. It can be described as a complicated variant of the chalcopyrite structure. Typical for Li-rich phases, Ba19Li44 contains icosahedron-based polytetrahedral clusters.