Maximizing thermoelectric performance in SnTe through strategic co-doping, nanostructuring, and topological insights

Abstract

Enhancing thermoelectric performance through doping is a pivotal strategy, optimizing carrier concentration, reducing energy band separation, and decreasing thermal conductivity. This study delves into the thermoelectric and magneto-transport properties of SnTe single crystals, recognized for their topological insulator characteristics. SnTe's unique electronic states, featuring highly conductive surface states protected by crystal symmetry, significantly boost electrical conductivity while maintaining low thermal conductivity. Consequently, a high thermoelectric figure of merit (ZT) of approximately 0.71 is achieved at 873 K along the (111) direction. By fine-tuning carrier concentration and employing nanostructuring techniques, we enhanced the ZT of pristine SnTe to 0.75 at 811 K. Additionally, we explored the co-doping effects of Mg, Ag, and Bi on the thermoelectric properties of self-compensated polycrystalline SnTe. Bi-doping effectively reduces carrier concentration, promotes valence band convergence, and lowers thermal conductivity. The co-doping of Bi and Ag induces valence band convergence, further amplified by Mg doping, resulting in high power factors of 20.7 and 22.8 μW cm⁻¹ K⁻² at 872 K in Sn_0.94Ag_0.03Bi_0.06Te and Sn_0.86Ag_0.03Mg_0.08Bi_0.06Te, respectively. The all-scale hierarchical structure and elemental doping significantly reduce lattice thermal conductivity to ultra-low values of 0.135 and 0.123 W m⁻¹ K⁻¹ at 873 K in Sn_0.94Ag_0.03Bi_0.06Te and Sn_0.86Ag_0.03Mg_0.08Bi_0.06Te, respectively. These combined effects yield high ZT values of approximately 1.6 and 2.01 at 873 K in Sn_0.94Ag_0.03Bi_0.06Te and Sn_0.86Bi_0.06Ag_0.03Mg_0.08Te, respectively. Moreover, we conducted de Haas–van Alphen (dHvA) studies to further elucidate the topological surface state properties of SnTe. These investigations enabled us to extract critical parameters such as the cyclotron effective mass, Fermi surface area, and Fermi velocity, offering deeper insights into the electronic structure and enhancing our understanding of the material's unique characteristics. Our findings highlight the significant potential of co-doping and nanostructuring strategies in advancing the thermoelectric performance of SnTe, paving the way for the development of high-efficiency thermoelectric materials.