Recently, SnSe has attracted wide attention as a promising environment-friendly IV-VI thermoelectric material. Here, SnS is alloyed with Na-doped SnSe to decrease the thermal conductivity for better thermoelectric performance. Consistent with previous reports, the lattice constant and the band gap change linearly with increasing SnS, suggesting the formation of SnSe1-xSx solid solution. However, SnS nano-precipitations have been clearly observed, indicating the phase separation in the alloys. Moreover, the grain size decreases obviously with increasing SnS amount. The first-principles calculations show that the nano-precipitation is due to the positive formation energies for SnSe1-xSx in the small x region. Due to the structure engineering, the lattice thermal conductivity is greatly reduced in SnSe1-xSx samples, leading to a promising ZT of 1.35 for Na0.03Sn0.97Se0.7S0.3 at 816 K. Keywords: SnSe, Solid solution, Grain refinement, Thermal conductivity, Thermoelectric performance
