Cubic phase stabilization and thermoelectric performance optimization in AgBiSe2–SnTe system

AgBiSe2 is a lead-free thermoelectric (TE) material that demonstrates excellent TE performance in its high-temperature cubic phase. However, the known order-disorder transition at around 580 K induces internal stress caused by the sudden change in thermal expansion coefficient, negatively impacting TE device operation. In this study, we heavily alloyed AgBiSe2 with SnTe to increase configurational entropy (ΔS) and maintain disordered cubic phase throughout the entire temperature range. This structure variation from hexagonal to cubic increased the density-of-state effective mass as demonstrated by experimental results and first-principles calculations. Additionally, the lattice thermal conductivity was reduced by multiple point defects. Overall, the average ZT value from 300 K to 773 K increased to 0.3 after SnTe alloying. Our study provides an additional perspective of entropy engineering on thermoelectric properties beyond the conventional phonon scattering, which helps to tailor properties in other TE materials with phase transition.