Synergistic optimization of thermoelectric performance of Sb doped GeTe with strained domain and domain boundaries
In addition to the Ge-vacancy control of GeTe, the Antimony (Sb) substitution of GeTe for the improvement of thermoelectric performance is explored for Ge1-xSbxTe between x=0.08-0.12. The concomitant carrier concentration (n) and the aliovalent Sb ion substitution led to an optimal doping level of x=0.10 to show ZT ~2.35 near ~800 K, which is significantly higher than those single- and multi-elements substitution studies of GeTe system reported in the literature. In addition, Ge0.9Sb0.1Te demonstrates an impressively high power factor of ~ 36 μWcm-1K-2 and low thermal conductivity of ~1.1 Wm-1K-1 at 800 K. The enhanced ZT level for Ge0.9Sb0.1Te is explained through a systematic investigation of micro-structural change and strain analysis from room temperature to 800 K. Significant reduction of lattice thermal conductivity (κlat) is identified and explained by the Sb substitution-introduced strained and widened domain boundaries for the herringbone domain structure of Ge0.9Sb0.1Te. The Sb substitution created multiple forms of strain near the defect centre, the herringbone domain structure, and the widened tensile/compressive domain boundaries to support phonon scattering that covers wide frequency range of phonon spectrum to reduce lattice thermal conductivity effectively.