SnTe is an exceptionally promising eco-friendly thermoelectric material that continues to draw immense interest as a source of alternative energy recovered from waste heat energy. Here, we investigate the effect of introducing Cu as a single doping element rather than phase separated in SnTe followed by Sb co-doping to tune the lattice thermal conductivity. A microstructure evolution was observed which influences the thermoelectric performance of these SnTe-based materials. An overall power factor of ∼22 μW/cmK 2 and an ultralow lattice thermal conductivity of 0.39 W/mK are reported. A maximum ZT of 0.86 is also reported with an all-time record high hardness value of 165 Hv among SnTe-based thermoelectric materials. Through DFT calculations, we show that Cu opens the band gap of SnTe, whereas Sb in the presence of Cu introduces resonance levels and causes band convergence. This kind of enhanced thermoelectric performance is paramount for the application of SnTe in recovery of heat into useful electrical energy.

The new paradigm for increasing the commercial viability of thermoelectric materials in the energy sector is the theoretical prediction and subsequent experimental validation and optimization of cheaper and inherently more efficient compositions. Herein, the experimental validation of the recently theoretically predicted ZrFe 0.50 Ni 0.50 Sb double half-Heusler and the ability to intrinsically tune this system to optimized p-or n-type materials by varying the Fe/Ni ratio in the synthesized ZrFe x Ni 1−x Sb (x = 0.35−0.65) samples are demonstrated. The samples are synthesized by arc melting, hot pressing, and annealing. Subsequent microstructural analysis confirms the crystallization of the ZrFe x Ni 1−x Sb into the half-Heusler structure and reveals that the variation of the Fe/Ni ratio favors the Ni-rich side. Consequently, the best p-type x = 0.55 and n-type x = 0.35 samples exhibit higher power factor values stemming from an increased carrier concentration, higher density of state effective mass, and suppressed bipolar conduction, as indicated by the Hall data analysis and density functional theory simulations. The additional lattice disorders introduced by varying the Fe/Ni ratio suppress the thermal conductivity and increase the microhardness of the n-type samples. The ZrFe 0.35 Ni 0.65 Sb and ZrFe 0.55 Ni 0.45 Sb samples achieve maximum zTs of ∼0.43 and 0.06, respectively, which is a great improvement over the ∼0.001 value of the ZrFe 0.50 Ni 0.50 Sb sample. These results highlight the viability of tuning the performance of double half-Heuslers on the doubly doped site. They will be instrumental in demonstrating the feasibility of developing low-cost double half-Heusler materials with better intrinsic and highly tunable properties.

Ongoing research and development focus on emerging thermoelectric materials with enhanced performance, continually making the possibility of waste heat recovery a reality. In this work, we engineer the thermoelectric properties of the layered SnSb2Te4 topological insulators. To date, there is little research reporting on these materials as potential state-of-the-art thermoelectric materials. Thus, there is a need to formulate effective strategies to realize this potential. Since these materials are known to have intrinsically low lattice thermal conductivity, we shift our attention to improving the electrical transport properties. For the first time, positional Bi doping at both the Sn and Sb cation sites is adopted. The aliovalent and isovalent nature of Bi at these sites, respectively, is shown to cause significant improvements in the performance of these layered materials. The electronic band structure of the pure and doped samples, where we considered various occupancies, is studied whereby we reveal the occurrence of band convergence and resonant levels resulting in a high power factor of ∼10.8 μW cm–1 K–2 at 623 K. Overall, a high ZT of ∼0.46 at a relatively lower temperature of 673 K is recorded. The potential of these materials for thermoelectric applications is shown, especially in the case of Bi doping at the Sn cation site. Continued efforts to enhance the thermoelectric performance of these topological insulators are needed for them to gain a substantial competitive edge in comparison to other state-of-the-art thermoelectric materials.