The large ZT is also driven by the intrinsically-low lattice thermal conductivities of 3.77 W m -1 K -1 at 600 K and 2.27 W m -1 K -1 at 1000 K. Due to the short phonon mean free paths, we predict that nanostructururing is unlikely to be a viable strategy for enhancing the ZT, as this only decreases the lattice thermal conductivity by 6% at 1000 K but decreases the power factor by an average of 18% depending on the charge-carrier concentration.