PbTe is known to be a promising thermoelectric material for waste heat recovery,so it has been the subject of extensive research and high thermoelectric performances have been obtained.Here,we will show the effect of microstructure on the thermoelectric properties.Firstly,we systematically investigate the relationship between nano grain size and TE properties.It is found that the thermoelectric figure of merit,zT,strongly depends on the synthesis condition and that its value can be enhanced to~2.0 at 773 K by optimizing the size distribution of the nanostructures in the material.The smallest sizes(2~6 nm)of nanostructures are responsible for effectively scattering the wide range of phonon wavelengths to minimize the lattice thermal conductivity to~0.5 W/m K.Therefore,the zT enhancement is attributed to the reduction of both the lattice and electronic thermal conductivities.Secondly,we propose a heterogeneous nanostructure for bulk thermoelectrics.By varying the quenching time of Na doped PbTe,followed by hot pressing,we synthesized heterogeneous nanocomposites,a mixture of nanodot nanocomposites and nanograined nanocomposites.It is found that figures of merit,zT,of those heterogeneous nanocomposites exhibited a zT around 2.0 at 773 K,which is a 25%increase compared to zT of a homogeneous nanodot nanocomposite in our experiment.The power factor increase is 5%,and the thermal conductivity reduction is 15%;thus,zT increase mainly comes from the thermal conductivity reduction.All in all,the thermoelectric properties is strongly depended on the microstructures and right nano grain size and heterogeneous nanostructure should be the better way to enhance the thermoelectric performance of bulk PbTe.