Chemical bonding origin of the thermoelectric power factor in Half-Heusler semiconductors

Abstract

Intermetallic semiconductors with the cubic Half-Heusler structure (XYZ) have excellent thermoelectric properties. This has been attributed to the high degeneracy of the carrier pockets in the band structure, but large differences are found between different material compositions. Half-Heuslers are often interpreted within Zintl chemistry, making a clear distinction between an electropositive cation ($X^{n+}$) and an extended polyanion ($Y{Z}^{n-}$). Based on quantitative real space chemical bonding analysis, we unravel large degrees of covalent bonding between the formal cation and anion, making the Zintl distinction clearly invalid. This covalence is shown to strongly affect the band structure, thermoelectric properties and response properties in the materials, with improved thermoelectric properties observed for those materials that least follow the Zintl concept. This expands our knowledge of the chemical bonding motifs governing physical properties, and gives a critical view on the simplistic chemical concepts too often applied for design of complex materials.

arXiv comment29 pages, 12 figures

References in corpus (10)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• BoltzTraP. A code for calculating band-structure dependent quantities
• Optimized norm-conserving Vanderbilt pseudopotentials
• Maximally localized Wannier functions: Theory and applications
• A beginner's guide to the modern theory of polarization
• The physics of dynamical atomic charges: the case of ABO3 compounds
• Relating chemical bonding to physical properties: The origin of unexpected isotropic properties in layered materials
• Electronic structure of Zr-Ni-Sn systems: role of clustering and nanostructures in Half-Heusler and Heusler limits
• A simple model for vacancy order and disorder in defective half-Heusler systems

Cited by in corpus (1)

• Enhanced thermoelectric properties of two-dimensional Janus ferromagnetic LaBrI with strain-induced valley degeneracy