Enhanced thermoelectric performance of double perovskites Ba2NbBiS6 and Ba2TaSbS6 via carrier engineering and chemical potential tuning

Abstract

The elastic and thermoelectric properties of Ba₂NbBiS₆ and Ba₂TaSbS₆ were investigated to assess their mechanical stability and thermoelectric efficiency. Elastic property calculations confirmed that both compounds satisfy the mechanical stability criteria. Ba₂TaSbS₆ exhibits a higher bulk modulus (127.34 GPa), shear modulus (54.92 GPa), and Young's modulus (139.83 GPa), indicating superior stiffness and hardness, while Ba₂NbBiS₆, with a lower bulk modulus (112.51 GPa) and shear modulus (48.76 GPa), demonstrates greater ductility, making it more adaptable for flexible applications.

Thermoelectric transport properties were analyzed as functions of temperature, carrier concentration, and chemical potential. At 900 K, Ba₂NbBiS₆ exhibited an initial ZT of 0.6090 at a carrier concentration of n₀ = −3.2920 × 10¹⁹ cm⁻³ and chemical potential μ₀ = 0.5411 Ryd, while Ba₂TaSbS₆ had a ZT of 0.4968 at n₀ = 0.9666 × 10¹⁹ cm⁻³ and μ₀ = 0.62138 Ryd. An increase in ZT was observed with temperature, attributed to enhanced charge carrier mobility and reduced lattice thermal conductivity. A systematic optimization of carrier concentration through controlled doping led to significant enhancements in ZT, reaching 0.9209 for Ba₂NbBiS₆ at n = −23.6592 × 10²¹ cm⁻³ and μ = μ₀ + 0.1782 Ryd, and 0.8646 for Ba₂TaSbS₆ at n = −1.6144 × 10²¹ cm⁻³ with μ = μ₀ + 0.1073 Ryd, representing increases of 51.2 % and 74.1 %, respectively. These findings highlight the potential of Ba₂NbBiS₆ and Ba₂TaSbS₆ for high-temperature thermoelectric applications, where a balance between mechanical stability and energy efficiency is crucial. Ba₂TaSbS₆ stands out as a mechanically robust material suitable for high-strength applications, while Ba₂NbBiS₆, with its enhanced ductility, is promising for flexible thermoelectric devices. Future studies should explore doping strategies and nanostructuring techniques to further enhance their thermoelectric properties for practical energy conversion applications.