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

The transport characteristics of high performance (AgxSbTex/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 similar to 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.