Explaining the electronic band structure of half-Heusler thermoelectric semiconductors for engineering high valley degeneracy

• Published in: MRS bulletin 2022, Vol.47 (6), p.573-583
• Main Authors: Brod, Madison K., Guo, Shuping, Zhang, Yongsheng, Snyder, G. Jeffrey
• Format: Article
• Language: English
• Subjects: Applied and Technical Physics; Brillouin zones; Characterization and Evaluation of Materials; Chemistry and Materials Science; Conduction bands; Convergence; Energy Materials; Materials Engineering; Materials Science; Nanotechnology; Review Article; Thermoelectricity; Valence band; Valleys
• ISSN: 0883-7694; 1938-1425
• DOI: 10.1557/s43577-022-00360-z

Half-Heusler compounds are attractive candidates for thermoelectric applications because they are inexpensive and have high thermal and mechanical stability. Band engineering to promote electronic structures with high valley degeneracy, N V , is known to be an effective method for enhancing thermoelectric performance. In half-Heusler thermoelectrics, the valence band maximum can be found at the Γ -, L-, or W-point in the Brillouin zone, and there are two competing low-lying conduction bands at the X-point. Consequently, there are routes to increase the valley degeneracy of both the conduction band (CB) and valence band (VB) edges that involve converging the competing band extrema, and it has been found that the strategies for achieving VB and CB convergence are quite similar. Here, we review the chemical origins of these band extrema (using ZrNiSn and NbFeSb as particular examples) and the recommended strategies for achieving high band convergence, and hence, high N V . Graphical abstract