The effect of spark plasma sintering parameters on the microstructure and thermoelectric properties of p-type Bi0.5Sb1.5Te3 alloys

Abstract

Bismuth telluride-based alloys are commonly employed as commercial thermoelectric materials at room temperature. This work explores the influence of SPS parameters such as temperature, pressure, and dwell time on the microstructure and thermoelectric properties of the p-type Bi₀.₅Sb₁.₅Te₃ alloys. In this context, the polycrystalline samples were synthesized by a solid-state reaction, followed by SPS within the 425–500 °C temperature range, under pressures between 40 and 50 MPa, and for 6–10 min. The structural investigation by X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed significant differences in lattice parameters, grain orientation, and defect concentrations compared to the SPS conditions. Thermoelectric properties, including electrical conductivity, Seebeck coefficient, thermal conductivity, and figure of merit (ZT), were thoroughly evaluated. The Seebeck coefficient was 217 μV K⁻¹, and electrical resistivity was optimized at 13.1 μΩ m. Thermal conductivity decreased with pressure to 0.77 W m⁻¹ K⁻¹, reflecting increased phonon scattering via microstructure optimization. The optimal sample, which was sintered at 500 °C, 46 MPa, and 8-min dwell time, exhibited a power factor of 3.5 mW/mK² and a peak zT value of 1.41 at 50 °C, which is a 16 % and 38 % improvement, respectively, compared with baseline samples. The results highlight the significance of optimizing SPS parameters to maximize the overall thermoelectric efficiency of Bi₂Te₃-based materials through the optimization of electrical and thermal transport properties.