Finding the order in complexity: The electronic structure of 14-1-11 zintl compounds

Yb14MnSb11 and Yb14MgSb11 have rapidly risen to prominence as high-performing p-type thermoelectric materials. However, the fairly complex crystal structure of A14MX11 Zintl compounds renders the interpretation of the electronic band structure obscure, making it difficult to chemically guide band engineering and optimization efforts. In this work, we delineate the valence-balanced Zintl chemistry of A14MX11 compounds using the molecular orbital theory. By analyzing the electronic band structures of Yb14MgSb11 and Yb14AlSb11, we show that the conduction band minimum is composed of either an antibonding molecular orbital originating from the (Sb3)7- trimer or a mix of atomic orbitals of A, M, and X. The singly degenerate valence band is comprised of non-bonding Sb pz orbitals primarily from the Sb atoms in the (MSb4)m- tetrahedra and of isolated Sb atoms distributed throughout the unit cell. Such a chemical understanding of the electronic structure enables strategies to engineer electronic properties (e.g., the bandgap) of A14MX11 compounds.