BiSbTe has been realized as an ideal p-type thermoelectric material near room temperature; however, its commercial applications are largely restricted by its n-type counterpart that exhibits relatively inferior thermoelectric performance. In this work, n-type BiTeSe based composites Bi₂Te_2.7Se_0.3–f InSb (0 ≤ f ≤ 2.5 vol%) are prepared by a ball milling and spark plasma sintering method. A record-high ZT value of ∼1.22 is achieved at 323 K for Bi₂Te_2.7Se_0.3–1.5 vol% InSb composites. This significant enhancement in thermoelectric performance is attributed to the incorporation of nanostructured InSb into the Bi₂Te_2.7Se_0.3 matrix, which can simultaneously modulate the electrical and thermal transport. InSb with high carrier mobility precipitated in the matrix can strengthen interface scattering at the phase boundaries, which can effectively scatter the heat-carrying phonons and thus yield an extremely low lattice thermal conductivity, while the high power factor is maintained. As a result, a maximum ZT of 1.22 is obtained. The average ZT in the temperature range of 300–425 K for Bi₂Te_2.7Se_0.3–1.5 vol% InSb is 1.14, which is at least 15% larger than that of previously reported values. Our results demonstrate that for n-type bismuth-telluride-based alloys, imbedding nanostructured phases with a high carrier mobility is an effective strategy for enhancing the performance of the state-of-the-art thermoelectric systems.

Two simplified chemical processes, a co-precipitation and a reduction method, were developed to synthesize pure Cu₂Se nanoparticles. The XRD results indicate that the co-precipitation method is a better way to synthesize high-purity Cu₂Se in comparison to the reduction method, where a small amount of Cu₂O and Cu are found. Scanning electron microscopy reveals that Cu₂Se powder synthesized by the reduction method possesses a morphology dominated by irregular hexagonal nanoplates and spherical nanoparticles; however, only nanoplates are observed in powder prepared by the co-precipitation method. The effect of the two synthetic methods on the thermoelectric properties of Cu₂Se, in the temperature range of 300–1000 K, was investigated. The results indicate that the co-precipitation method subsequently combined with a hot-press process, is an effective way to improve Cu₂Se thermoelectric performance compared to the reduction method together with hot-pressing. The largest figure of merit, ZT, for Cu₂Se fabricated by the co-precipitation method is 1.35, which is 40% larger than that of Cu₂Se fabricated by the reduction method (ZT_max = 0.97) due to its good power factor at high temperatures.

Through incorporation of isostructural Bi₂Te₃ nanoinclusions in n-type Bi₂Te_2.7Se_0.3 we achieve unprecedented energy-conversion efficiency η = 10.5% with record high ZT_max = 1.35.