Nanostructures in high-performance (GeTe)x(AgSbTe2)100-x thermoelectric materials

The thermoelectric properties of (GeTe)(x)(AgSbTe(2))(100-x) compounds (x = 75, 80, 85 and 90; TAGS-x) have been studied as a function of temperature from 300 to 720 K. At 720 K the dimensionless figure of merit ZT reaches the state-of-the-art value of 1.53 for TAGS-75 and 1.50 for TAGS-80 and TAGS-85 samples, respectively. But the ZT value of the TAGS-90 sample is only 0.50 at 720 K due to the high carrier concentration. Utilizing high-resolution transmission electron microscope and selected area electron diffraction techniques, we identify a considerable number of nanoscale domains with typical size similar to 10 nm in the samples that show high ZT values. It is suggested that the presence of nanoscale domains, like the situation in PbTe-AgSbTe(2) compounds, should make a slight contribution to the low lattice thermal conductivity of TAGS compounds due to the enhanced mid-frequency phonon scattering.