Room temperature Bi₂Te₃-based thermoelectric materials with high performance

Several off-stoichiometric compositions Bi_0.5Sb_1.5+xTe_3+δ (x = 0.2; δ = 0, 0.12, 0.14) were deliberately synthesized to produce in-situ composites based on compositional engineering approach. The structural characterization of these materials employing XRD, SEM, and HR-TEM reveals the formation of in-situ-composites containing Bi_0.5Sb_1.5Te₃ as matrix phase and minor phases of either Sb rich or Te rich in different compositions. Thermoelectric properties of these Bi_0.5Sb_1.5+xTe_3+δ (x = 0.2; δ = 0, 0.12, 0.14) composites were studied in a wide range of temperatures extending from room temperature to 500 K. The electronic transport of these composites exhibits p-type semiconducting materials. The lowest thermal conductivity of ~ 0.69 W/m K @310 K was observed for Bi_0.5Sb_1.7Te_3.12 composite, which was noted to be 14% reduced thermal conductivity when compared with that of the state-of-the-art Bi_0.5Sb_1.5Te₃ (κ\(=\) 0.82 W/m K) material. In addition to this, an enhanced power factor was also observed in Bi_0.5Sb_1.7Te_3.12 which is primarily due to increased electrical conductivity of these materials. This enhanced power factor of the composition of Bi_0.5Sb_1.7Te_3.12 coupled with reduced thermal conductivity yields to high ZT ~ 1.13 at nearly room temperature, making these materials viable for large scale applications.