Coherent Nanointerfaces in Thermoelectric Materials

In recent years, a new type of bulk nanostructured thermoelectric material Ag 1− x Pb m SbTe 2+ m (LAST) has been developed featuring significantly improved figure of merit ( ZT ) (up to 2.1 at 800 K). Its excellent ZT is largely attributed to the nanoscale coherent interface that promotes phonon scattering while having minimal effect on electron transport. Despite the experimental work on LAST material synthesis and characterization, very little knowledge is known about the nanoscale coherent interface and its effect on energy transport. In this work, we report on the first atomic observation of coherent nanointerface in a PbTe/GeTe nanocomposite and quantitative characterization of the local chemical composition and crystalline structure based on atomistic modeling. The structure coherency is confirmed with atom position imaging, atom number density distribution, and line and point coherency functions. Lattice matching occurs at the interface with lattice twisting and extremely localized strain (ϵ ≈ 0.007) in a region of 5−6 nm in GeTe. The localized strain field also helps reduce the thermal transport in the material. The effective lattice thermal conductivity of the nanocomposite at 700 K is calculated at 1.23 W m −1 K −1, which is lower than that of many common thermoelectric materials. The low interfacial thermal resistance 7.3 ± 0.3 × 10 −10 m 2 K W −1 illustrates weak interface phonon scattering by the coherent interface structure. This coherent interface is credited with very little electrical conductivity reduction, which is crucial for design of high ZT thermoelectric materials.