A family of new compounds derived from chalcopyrite. common patterns in their electronic and crystal structures

A series of new compounds has been synthesized by insertion of alkali or al kaline earth-metals in chalcopyrite, CuFeS2. Their crystal structures vary from layered arrangements of tetrahedra in a trigonal (LiCuFeS2, NaCuFeS2) or a tetragonal symmetry (KCuFeS2, CsCuFeS2), to three-dimensional cubic fr amework (BasCu(12)Fe(13)S(27)). Despite these differences, the synthesized compounds follow a common structural pattern: the sulfur and M atoms (M= Li , Na, K, Cs, or Ba) are ordered in a distorted face-centered-cubic lattice, where all tetrahedral holes surrounded by S atoms are occupied by the tran sition metal elements. The tetrahedral holes surrounded by both S atoms and at least one M element are empty. The band structures of these compounds a re discussed in the framework of an extended Huckel Hamiltonian.