Microscopic origin of the extremely low thermal conductivity and outstanding thermoelectric performance of BiSbX3 (X = S, Se) revealed by first-principles study.In this paper, we performed comprehensive investigations of both the thermal and electrical transport properties of BiSbSe3 and BiSbS3 by using first-principles calculations and Boltzmann transport theory.  As a result, these two materials possess extremely low lattice thermal conductivities.  Meanwhile, both BiSbSe3 and BiSbS3 exhibit similar anisotropic thermal transport behaviors, which is due to the smaller phonon group velocities along the a axis.  Our calculations provide insights into the origin of the extremely low thermal conductivity in BiSbSe3 and BiSbS3, which is meaningful for exploiting high performance thermoelectric materials with low thermal conductivity.
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