Ultralow Thermal Conductivity, Enhanced Mechanical Stability, and High Thermoelectric Performance in (GeTe)1-2x(SnSe)x(SnS)x

Thermoelectric (TE) energy conversion demands high performance crystalline inorganic solids that exhibit ultralow thermal conductivity, high mechanical stability, and good TE device properties. Pb-free germanium telluride (GeTe)-based material has recently attracted significant attention in TE power generation in mid temperatures, but pristine GeTe possesses significantly higher lattice thermal conductivity (kappa(latt)) compared to that of its theoretical minimum (kappa(min)) of similar to 0.3 W/mK. Herein, we have demonstrated the reduction of kappa(latt) of (Ge-Te)(1-2x)(SnSe)(x)(SnS)(x) very near to its kappa(min). The (Ge-Te)(1-2x)(SnSe)(x)(SnS)(x) system behaves as a coexistence of pointdefect rich solid solution and phase separation. Initially, the addition of equimolar SnSe and SnS in the GeTe reduces the kappa(latt) by effective phonon scattering because of the excess point defects and rich microstructures. In the second step, introduction of Sb-doping leads to additional phonon scattering centers and optimizes the p-type carrier concentration. Notably, 10 mol % Sb-doped (GeTe)(0)(.9)(5)(SnSe)(0.025)(SnS)(0.025) exhibits ultralow kappa(latt) of similar to 0.30 W/mK at 300 K. Subsequently, 10 mol % Sb-doped (GeTe)(0.95)(SnSe)(0.025)(SnS)(0.025) exhibits a high TE figure of merit (zT) of similar to 1.9 at 710 K. The high-performance sample exhibits a Vickers microhardness (mechanical stability) value of similar to 194 H-V that is significantly higher compared to the pristine GeTe and other state-of-the-art thermoelectric materials. Further, we have achieved a high output power, similar to 150 mW for the temperature difference of 462 K, in single leg TE device based on 10 mol % Sb-doped (GeTe)(0.95)(SnSe)(0.023)(SnS)(0.02)(5).