From synthesis to device: comparative study of Bi2Te3 alloys prepared by direct melt and ball milling for printed thermoelectrics

Abstract

The synthesis route of thermoelectric (TE) materials strongly influences their microstructure and transport properties. However, few studies compare different synthesis processes of Bi₂Te₃-based alloys and their impact on the microstructure and thermoelectric properties of the resulting materials. Here, we compare n-type and p-type Bi₂Te₃-based alloys prepared via high-energy ball milling and direct melt processes. Ball milling is a simpler, low-cost, room-temperature process that eliminates the need for high-temperature furnaces. The direct melting method used here closely resembles commercial melting techniques for polycrystalline materials. In this study, both routes yielded TE materials with similar crystallinity, morphology, and phase purity. The powders obtained were then converted into binder-free printable inks. At 300 K, the measured ZT ranged from 0.1 to 0.5, limited by low electrical conductivity, while a high Seebeck coefficient and low thermal conductivity (0.2–0.3 W m⁻¹ K⁻¹) were achieved. Energy consumption analysis indicates that ball milling requires 3–5 times less energy per gram than melt synthesis. Planar thermoelectric generators (PTEGs) were fabricated on a polyimide substrate by a simple four-step process, using the inks derived from both synthesis routes. The milled-material PTEG exhibited an open-circuit voltage of 86.7 mV at ΔT = 40 K and delivered a higher power output than the melt-material device, due to the lower electrical resistance achieved at the device level. This work demonstrates that high-energy ball milling provides a scalable and energy-efficient route to printable thermoelectric materials, enabling low-grade temperature energy harvesting applications.