The interplay of chemical bonding and thermoelectric properties in doped cubic GeTe

Abstract

GeTe-based alloys hold great promise for thermoelectric applications. Our comprehensive study investigates the intricate interplay between chemical bonding and transport properties in cubic GeTe. We demonstrate a balance between minimizing thermal conductivity and maximizing power factor, guided by the mediating influence of chemical bonding. Our primary findings reveal that Pb-doped GeTe exhibits low lattice thermal conductivity due to weak p–p orbital interactions, whereas In-doping boosts lattice thermal conductivity by reinforcing the chemical bonds, as elucidated by crystal orbital hamilton population (COHP) analysis. Further investigation reveals weak s–p interactions in Bi-, Sb-, and Pb-doped GeTe, and strong s–p interactions in In-doped GeTe compared to the pure GeTe, as probed by projected density of state (PDOS). These dual effects explain the experimentally observed high power factor and enhanced zT in Bi-, Sb-, and Pb- doping in contrast to In-doping. In our study, we find that weak s–p interactions improves electronic performance by modifying DOS whereas weak p–p interactions reduce thermal transport by diminishing the strength of chemical bonding. These findings underscore the correlation between doping-induced modifications in chemical bonding and resulting thermoelectric properties. Utilizing a first-principles framework, we systematically explore the temperature and carrier concentration-dependent transport properties of pure GeTe under relaxation time approximation. Optimization strategies yield a maximum peak power factor times temperature of 2.2 Wm⁻¹ K⁻¹ and a maximum zT value of ∼0.83 at 800 K, showcasing the potential for tailored thermoelectric performance. Finally, this research presents a systematic approach to improve thermoelectric performance by modifying chemical bonds through doping.