Enhancing Thermoelectric Properties of Bi₂Te₃-Based Pellets through Low-Temperature Liquid Phase Sintering and Heat Treatment

Abstract

Low-temperature liquid phase sintering (LPS) has proven to be cost effective in preparing Bi 2 Te 3 -based pellets with promising thermoelectric properties. The previous work explored deionized water as the transient liquid phase with a low boiling point (100 °C), making it challenging to produce densified pellets at high temperatures. In this work, we opted for an ethylene glycol (EG) solution with a higher boiling point (∼200 °C) as the liquid phase. The EG solution serves as a suitable alternative and enhances the electrical conductivity and power factor of n-type Bi 2 Te 2.7 Se 0.3 (BTS) materials. Moreover, the BTS samples were heat treated to assess the effectiveness in increasing the ZT value. The BTS samples subjected to LPS with 3% EG addition and followed by a heat treatment at 300 °C exhibited a power factor of 1056 μW/mK 2 . A lattice thermal conductivity of 0.69 W/mK was achieved at room temperature, originating from enhanced phonon scattering by enriched grain boundaries and other crystal defects. These samples demonstrate a maximum ZT value of 0.43 at 381 K, ∼72% improvement over the deionized water-treated samples (ZT max = 0.25). The findings highlight the significance of liquid phase selection and heat treatment in optimizing the thermoelectric properties of the BTS materials.