Crystal structure of the ‘missing’ inter­metallic compound BaCu5

Abstract

The copper-rich inter­metallic compounds CaCu₅ and SrCu₅ are isostructural but the isomorphous compound BaCu₅ (barium penta­copper) has not been reported. The absence of any compound with the composition of BaCu₅ in the Ba–Cu phase diagram has previously been attributed to much larger radius of Ba. The structure of BaCu₅, which crystallizes in an ortho­rhom­bic cell (space group Pnma) with the rare SrZn₅ 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.

The copper-rich inter­metallic compounds CaCu₅ and SrCu₅ are isostructural but the isomorphous compound BaCu₅ (barium penta­copper) has not been reported. The absence of any compound with the composition of BaCu₅ in the Ba–Cu phase diagram has previously been attributed to much larger radius of Ba. The structure of BaCu₅, which crystallizes in an ortho­rhom­bic cell (space group Pnma) with the rare SrZn₅ 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.