Finding the Order in Complexity: The Electronic Structure of 14-1-11 Zintl Compounds

Abstract

Yb14MnSb11 and Yb14MgSb11 have rapidly risen to prominence as high-performing p-type thermoelectric materials for potential deep space power generation. However, the fairly complex crystal structure of 14-1-11 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 (A = Yb, Ca; M = Mg, Mn, Al, Zn, Cd; X = Sb, Bi) using molecular orbital theory analysis. 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 p-z orbitals primarily from the Sb atoms in the (MSb4)m- tetrahedra and the 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 band gap) of A14MX11 compounds.