Crystal structure of the ‘missing’ intermetallic compound BaCu 5

The copper-rich intermetallic compounds CaCu 5 and SrCu 5 are isostructural but the isomorphous compound BaCu 5 (barium pentacopper) has not been reported. The absence of any compound with the composition of BaCu 5 in the Ba–Cu phase diagram has previously been attributed to much larger radius of Ba. The structure of BaCu 5 , which crystallizes in an orthorhombic cell (space group Pnma ) with the rare SrZn 5 structure type is now reported The structure is characterized by a zigzag arrangement of infinite Ba chains ensconced in a Cu matrix. The Ba atom and three Cu atoms lie on special positions with m site symmetry and one Cu atom lies on a general crystallographic position.