Realize High Thermoelectric Properties in n-Type Bi₂Te_2.7Se_0.3/Y₂O₃ Nanocomposites by Constructing Heterointerfaces

Due to the excellent thermoelectric performance, bismuth telluride (Bi₂Te₃) compounds are highly promising for the thermoelectric conversion in the room temperature range. However, the inferior thermoelectric performance of the n-type leg severely restricts the applications of Bi₂Te₃-based thermoelectric couples. Herein, n-type Bi₂Te_2.7Se_0.3 (BTS)-based thermoelectric materials incorporated with nanosized Y₂O₃ (0.5-3 wt %) are prepared and their thermoelectric properties are systematically studied. The dramatically improved thermoelectric performance is ascribed to the realization of a multiscale feature of Y₂O₃ nanoparticle (NP)-induced interfacial decorations distributed along grain boundaries, which creates massive BTS/Y₂O₃ interfaces for the manipulation of carrier and phonon transport properties. The geometric phase analysis is employed to further confirm the condition of local strain in the BTS composite incorporated with Y₂O₃ NPs. Due to the presence of heterointerfaces and high density of dislocations in BTS matrices, the minimum lattice thermal conductivity (κ_l) of the nanocomposites (NCs) is dramatically suppressed from 0.76 to 0.37 W m^-1 K^-1. With the incorporation of 3 wt % Y₂O₃ NPs, the Vickers hardness of the BTS/Y₂O₃ NC is increased by about 32%. Overall, the BTS + 1.5 wt % Y₂O₃ NC maintains excellent thermoelectric properties (ZT_ave = 1.1) in the whole operative temperature range (300-500 K). The present strategy of implementing high-density heterogeneous interfaces by Y₂O₃ NP addition offers an applicable pathway for fabricating high-performance thermoelectric materials with both optimized thermoelectric properties and mechanical properties.