Microstructure engineering beyond SnSe_(1-x)S_(x)solid solution for high thermoelectric performance

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 Na_(0.03)Sn_(0.97)Se_(0.7S0.3)at 816 K.