High solubility of Al and enhanced thermoelectric performance due to resonant states in Fe2VAlx

Recently, n-type Fe2VAl-based full-Heusler systems, exhibiting high thermoelectric power factors, have sparked new interest in this material class for thermoelectric applications. In this paper, the aluminum-rich region of the L2(1) phasespace in Fe-V-Al is explored by a step-by-step increase in the Al content in Fe2VAlx. We reveal a promising route to improve the thermoelectric properties of p-type Heusler alloys. First, we find an ultrahigh solubility of Al in Fe2VAlx and confirm the presence of a single Heusler phase up to x = 2 using x-ray diffraction analysis and scanning electron microscopy. Second, thermoelectric transport properties, measured in a wide temperature range from 4 to 800 K, show a substantial increase in the thermopower by over 100% and a significant decrease in the thermal conductivity by up to 80% for the Al-rich samples. Detailed analysis of the carrier-concentration-dependent thermopower as well as Hall measurements indicate the formation of a resonant state at the valence band edge as a likely origin for this enhancement. This is further corroborated by density-functional-theory calculations of the electronic density of states. Our work sets the stage for p-type full-Heusler materials with enhanced thermoelectric performance, applying the principle of resonant states to this material class. (c) 2022 Author(s).

Automated summary

This paper explores the aluminum-rich region in the Fe-V-Al material system and proposes a promising approach to improve the thermoelectric properties of p-type Heusler alloys. Experimental results show that Fe2VAlx alloys with high Al solubility exhibit significantly increased thermopower and reduced thermal conductivity. The analysis suggests that the enhancement is likely attributed to the formation of a resonant state at the valence band edge, which is supported by density-functional-theory calculations. This work paves the way for the development of p-type full-Heusler materials with enhanced thermoelectric performance.