Enhanced thermoelectric performance enabled by compositing ZrO₂ in n-type SiGe alloy with low thermal conductivity

SiGe-based thermoelectric (TE) materials have gained increasing interests due to their low maintenance costs, environmental friendliness and long lifespan. However, the intrinsically high thermal conductivity of Si-based materials also results in poor TE properties. In this investigation, a zirconia (ZrO₂) composite strategy was applied to an n-type SiGe alloy, tremendously elevating its TE performance. After mechanical alloying and spark plasma sintering (SPS) processes, the ZrO₂ induced the formation of nanopores in the SiGe matrix via phosphorus adsorption. Moreover, such increase in porosity enhanced the phonon scattering and dramatically suppressed lattice thermal conductivity, from 2.83 to 1.59 W·m⁻¹·K⁻¹ at 873 K. Additionally, reduced phosphorus doping led to an increase in Seebeck coefficients and a relatively minor decrease in electrical conductivity. The power factor didn’t deteriorate significantly, either, as its maximum of ~ 3.43 mW·m⁻¹·K⁻² was achieved at 873 K with (Si_0.8Ge_0.2)_0.097P_0.03(ZrO₂)_0.003. In short, a peak figure of merit (ZT) of ~ 1.27 at 873 K and an average ZT ~ 0.7 from 323 to 873 K were obtained. This study demonstrates that the electrical and thermal transportation of SiGe material can be synergistically tuned by compositing ZrO₂, illustrating a novel strategy to optimize the TE properties of bulk materials.