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

Abstract

Yb 14 MnSb 11 and Yb 14 MgSb 11 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 valencebalanced Zintl chemistry of A 14 M X 11 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 Yb 14 MgSb 11 and Yb 14 AlSb 11 , we show that the conduction band minimum is composed of either an antibonding molecular orbital originating from the (Sb 3 ) 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 (MSb 4 ) mtetrahedra 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 A 14 M X 11 compounds.

New Zintl Phase Yb10MgSb9 with High Thermoelectric Performance

“…One such example of a Zintl thermoelectric material is the Yb 14 M Sb 11 (14‐1‐11) compound, where M = Mn, Mg, Zn. [ 20–22 ] These 14‐1‐11 compounds have an inherently low, glass‐like thermal conductivity [ 23 ] with multi‐band complex Fermi surfaces [ 24 ] that lead to the best high‐temperature zT exceeding 1, suitable for use in thermoelectric generators for space applications. [ 25 ]…”

“…One such example of a Zintl thermoelectric material is the Yb 14 MSb 11 (14-1-11) compound, where M = Mn, Mg, Zn. [20][21][22] These 14-1-11 compounds have an inherently low, glass-like thermal conductivity [23] with multi-band complex Fermi surfaces [24] that lead to the best high-temperature zT exceeding 1, suitable for use in thermoelectric generators for space applications. [25] The exploration of other Yb-M-Sb (M = Mn, Mg, Zn) Zintl antimonide materials with different structures than 14-1-11 has also led to promising thermoelectric materials including Yb 21 Mn 4 Sb 18 , [26] Yb 9 Mn 4+x Pn 9 (Pn = Bi, Sb), [27][28][29] YbMnSb 2 , [30] and YbMg 2 Sb 2 .…”

Automated Bonding Analysis with Crystal Orbital Hamilton Populations

“…The band structure of the compound in the nonmagnetic state has been recently studied [59] . Similarly, an analysis of the band structure of Yb 14 Mg 1 Sb 11 crystallizing in the same type of structure, has been carried out [60] . The magnetism in Yb 14 MnSb 11 has also already been studied both experimentally and theoretically [61] .…”

“…[54] Similarly, an analysis of the band structure of Yb14Mg1Sb11 crystallizing in the same type of structure, has been carried out. [55] The magnetism in Yb14MnSb11 has also already been studied both experimentally and theoretically. [56] From previous studies, we expect an influence of the Mn-Sb bonds on the magnetism.…”

“…[59] Similarly, an analysis of the band structure of Yb 14 Mg 1 Sb 11 crystallizing in the same type of structure, has been carried out. [60] The magnetism in Yb 14 MnSb 11 has also already been studied both experimentally and [58] and automatic analysis of the conventional cell for CaTaO 2 N. We have enlarged the Ta environment. The code is able to automatically determine relevant bonds, coordination environments and average bond strengths (average ICOHPs); note that more negative ICOHPs indicate stronger bonds.…”