Multi-scale hierarchical microstructure modulation towards high room temperature thermoelectric performance in n-type Bi2Te3-based alloys

Bi2Te3-based thermoelectric materials are widely used in near room temperature refrigeration filed. Although Bi2Te3-based polycrystals prepared by powder metallurgy method exhibit good mechanical properties, the low room temperature dimensionless figure of merit (zT) for n-type alloys restricts their further usage. In this work, the electrical and thermal transport properties are manipulated synergistically by multi-scale hierarchical microstructure modulations in n-type Ag2Te/Bi2Te3 composites, including atomic-scale extrinsic point defects, nano-scale low-angel grain boundaries, mesoscale precipitate, and texturing. The carrier concentration is optimized by extrinsic point defects and the carrier mobility is improved due to the strengthened texture, and thus the power factor reaches a high value of 3.6 × 10−3 Wm−1/K2, which is even higher than the hot deformed counterparts. Simultaneously, the phonon scattering is enhanced by the multi-scale defects and the lattice thermal conductivity is suppressed. A high room temperature zT of ∼1.0 and an average zT of 0.96 in the 300–500 K range with good mechanical properties are obtained without hot deformation. This work puts forward a paradigm of enhancing the thermoelectric properties via multi-scale hierarchical microstructure modulations and is significant to the industrialization of manufacturing Bi2Te3-based alloys and devices.