Abstract
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.
Highlights
Yb14MnSb11 and Yb14MgSb11 have rapidly risen to prominence as high-performing p-type thermoelectric materials for potential deep space power generation
The energy conversion efficiencies of current thermoelectric devices remain insufficient for widespread applications
To obtain a large zT, a large Seebeck coefficient (α) and electrical conductivity (σ) are desired, while the thermal conductivity (κ) should be minimized. Because these properties are highly interrelated and all good thermoelectric materials behave as heavily doped semiconductors[2], engineering zT is best understood as optimizing the charge carrier concentration n and maximizing the thermoelectric quality factor B ∼ μW/κL where μW is the weighted mobility[3] and κL is the lattice thermal conductivity
Summary
Yb14MnSb11 and Yb14MgSb11 have rapidly risen to prominence as high-performing p-type thermoelectric materials for potential deep space power generation. We will focus on interpreting the computed band structures of two Yb14M Sb11 compounds: Yb14MgSb11 and Yb14AlSb11 using the Zintl concept in combination with a molecular orbital analysis.
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