Cold-Sintered Bi₂Te₃-Based Materials for Engineering Nanograined Thermoelectrics

Bi2Te3-based compounds are currently the most commercially relevant thermoelectric materials near room temperature. They are prepared via hot pressing, hot deformation, spark plasma sintering, and other consolidation processes, which are typically performed at 400–500 °C. Such high-temperature processes are energy-intensive and generate unnecessary waste heat, making them undesirable for a large-scale production. In this study, a low-temperature liquid-phase-assisted sintering (or so-called cold-sintering) process was employed to fabricate p-type Bi0.5Sb1.5Te3 bulk materials at temperatures below 150 °C. At the optimal sintering temperature (130 °C), a ZT value as high as 0.56 at 450 K can be achieved, competitive to that of a commercial Bi0.5Sb1.5Te3 ingot (ZT 0.8–1.0). The addition of a small amount of transient liquid facilitates grain reorientation and expedites a mass transfer process under axial compaction and liquid evaporation conditions, thus resulting in nearly fully densified Bi0.5Sb1.5Te3 pellet samples (>97% theoretical density). Furthermore, the low-temperature sintering process results in the reduction of grain size and promotes twin boundaries, resulting in a low lattice thermal conductivity of 0.57 W m–1 K–1 at 380 K due to phonon scattering. The strategy reported in this work can be used not only as a substitute for high-temperature sintering of other thermoelectric materials but also to engineer phonon scattering for high-performance thermoelectrics.