Synergistic optimization of thermoelectric performance of Sb doped GeTe with a strained domain and domain boundaries

Abstract

In addition to the Ge-vacancy control of GeTe, the antimony (Sb) substitution of GeTe for the improvement of thermoelectric performance is explored for Ge_1−xSb_xTe with 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-element substitution studies of the GeTe system reported in the literature. In addition, Ge_0.9Sb_0.1Te demonstrates an impressively high power factor of ∼36 μW cm⁻¹ K⁻² and a low thermal conductivity of ∼1.1 W m⁻¹ K⁻¹ at 800 K. The enhanced ZT level for Ge_0.9Sb_0.1Te is explained through a systematic investigation of micro-structural change and strain analysis from room temperature to 800 K. A significant reduction of lattice thermal conductivity (κ_lat) is identified and explained by the Sb substitution-introduced strained and widened domain boundaries for the herringbone domain structure of Ge_0.9Sb_0.1Te. The Sb substitution created multiple forms of strain near the defect centre, the herringbone domain structure, and widened tensile/compressive domain boundaries to support phonon scattering that covers a wide frequency range of the phonon spectrum to reduce lattice thermal conductivity effectively.