Enhancing the thermoelectric performance of GeTe through Sb doping and nanocompositing with SiC for reduced thermal conductivity

Abstract

Thermal conductivity (κ) is a crucial parameter in determining the thermoelectric figure of merit, zT, of thermoelectric materials. Consequently, numerous innovative strategies have been developed in recent years to reduce κ to the glass-like limit for enhanced thermoelectric properties. In this study, we employ a donor-like dopant, Sb, in GeTe to decrease both the electronic and lattice thermal conductivity. By reducing the hole concentration to 1.4 × 10²⁰ cm⁻³ in Ge_0.92Sb_0.08Te, we achieve a significantly low electronic thermal conductivity of 0.56 W m⁻¹ K⁻¹ at room temperature. Additionally, the strain and mass field fluctuations resulting from the presence of impurity atoms strengthen phonon scattering, effectively suppressing the lattice thermal conductivity. Furthermore, SiC nano-composites are intentionally introduced into the matrix, which leads to grain refinement. The grain boundaries and phase boundaries also contribute significantly to the reduction of lattice thermal conductivity, ultimately resulting in a small value of 0.42 W m⁻¹ K⁻¹ for the sample Ge_0.92Sb_0.08Te + 0.2 wt% SiC at room temperature. The Vickers hardnesses for all composite samples are measured which reveal strengthened hardness, thanks to the grain refinement. The improved peak zT for the Ge_0.92Sb_0.08Te + 0.2 wt% SiC sample is mostly attributed to the multiple reductions in κ. Through simulation, a high power density of 36 mW has been achieved for a single-leg Ge_0.92Sb_0.08Te + 0.2 wt% SiC thermoelectric device with a temperature difference of ΔT = 438 K. Our contribution demonstrates that elemental doping combined with nanocompositing can effectively suppress the thermal conductivity from room temperature to high temperature, beneficial for enhanced thermoelectric properties.