Roles of cations, electronegativity difference, and anionic interlayer interactions in the metallic versus nonmetallic character of Zintl phases related to arsenic

A first-principles Density Functional Theory study of several layered solids structurally related to rhombohedral arsenic has been carried out. The electronic structures of rhombohedral arsenic. CaSi2, CaAl2Si2, KSnSb, and SrSn2As2 are discussed in detail, emphasizing on the origins of their metallic or nonmetallic behaviours. It is found that all of these systems are metallic except KSnSb. Electronegativity differences between the elements in the anionic sublattice and/or direct interlayer interactions play the main role in controlling the conductivity behavior. CaSi2 exhibits a peculiar feature since the cation directly influences the conductivity but is not essential for its appearance. Cation-anion interactions are shown to have an important covalent contribution, but despite this fact and the metallic character found for most of these phases, the Zintl approach still provides a valid approximation to their electronic structure. (C) 2009 Wiley Periodicals, Inc.