Contrasting thermoelectric properties in cubic SnSe-NaSbSe2 and SnSe-NaSbTe2: High performance achieved via increasing cation vacancies and charge densities

Cubic SnSe has been recognized as one of the most promising mid-temperature thermoelectric candidates. Herein, the cubic-phase SnSe has been stabilized at room temperature by alloying NaSbSe2 and NaSbTe2, respectively, and the contrasting thermoelectric properties of SnSe-NaSbSe2 and SnSe-NaSbTe2 were systematically investigated. NaSbTe2-alloyed SnSe demonstrates better performance with especially higher electrical properties. According to the DFT calculations, the introduction of NaSbTe2 can bring the lattice parameter of cubic-phase SnSe closer to SnTe, leading to a lower cation vacancy formation energy and producing an ultra-high hole carrier concentration. Meanwhile, Te has a more developed charge density compared with that of Se, providing additional channels for charge transport when bonded to Sn atoms in cubic lattice. Limited by the electrical transport properties, the ZT(max) for SnSe-NaSbSe2 only reaches similar to 0.50 at 773 K, while the ZT(max) for SnSe-NaSbTe2 approaches similar to 0.95. Furthermore, sodium doping was utilized to tune the carrier mobility and carrier concentration of SnSe-NaSbTe2. Resultantly, the PFmax and ZT(max) values reach similar to 11 mu W cm(-1) K-2 and similar to 1.20 at 773 K in sodium-doped SnSe-NaSbTe2, 4.4 and 3.0 times higher than those of pure SnSe, respectively. Our study further promotes cubic-phase SnSe thermoelectrics for mid-temperature energy harvesting applications.