Ioffe–Regel limit and lattice thermal conductivity reduction of high performance (AgSbTe2)15(GeTe)85 thermoelectric materials

Abstract

The transport characteristics of high performance (Ag_xSbTe_x/2+1.5)₁₅(GeTe)₈₅ (TAGS-85) (x = 0.4–1.2) thermoelectric alloys are investigated. It is found that the carrier mean free path of TAGS-85 materials is comparable to the lattice parameter, indicating that this system has reached the minimum possible mobility, the Ioffe–Regel limit, and that further reduction of grain size will not affect the mobility while benefiting to the thermal conductivity reduction. The fine-grained samples are prepared by melt spinning to corroborate the supposition. The carrier mobility and mean free path of melt spun samples are indeed comparable with those of coarse-grained samples, while the lattice thermal conductivity is suppressed effectively as a result of the increasing boundaries and hence phonon scattering. A state-of-the-art ZT of ∼1.6 is obtained for the melt-spun fine-grained samples and the temperature region of ZT > 1.2 has been broadened notably, which is pretty encouraging for the future applications.