(Bi2Te3)0.2(Sb2Te3)0.8 (BST) based nanocomposites dispersed with amorphous SiO2 (a-SiO2) nanoparticles (∼50 nm) were fabricated and their thermoelectric properties were investigated in the temperature range from 293 K to 490 K. The results indicate that with increasing volume fraction of a-SiO2 from f = 0 to 0.55, 1.10, and then to 2.20 vol. %, the electrical resistivity ρ of the nanocomposites f(a-SiO2)/BST decreases first (f = 0.55 vol. %) and then increases rapidly with further increasing a-SiO2 content, which is proved to be caused mainly by changes of carrier concentration. In contrast, Seebeck coefficient S for the nanocomposites increases monotonically with increase in f, specially at T < ∼380 K, suggesting that at low a-SiO2 (f = 0.55 vol. %) content, at least, the increase in S of the nanocomposite could be ascribed to energy filtering effect arising from enhanced carrier scattering by the interface potentials due to the embedded a-SiO2 nanoparticles. Owing to both increased power factor (S2/ρ) and reduced thermal conductivity caused by phonon scattering of nanoparticles as well as phase boundaries, the dimensionless figure of merit ZT of f(a-SiO2)/BST composite sample with f = 0.55 vol. % enhanced substantially at T < 390 K; specifically, ZT of the composite sample reaches 1.12 and 1.27 at ∼303 K and ∼363 K, respectively, which is, respectively, ∼27% and ∼20% larger than that (0.88 and 1.06) of BST, demonstrating that thermoelectric performance of BST can be effectively elevated by incorporation of a-SiO2 nanoparticles.
Polypyrrole (PPy) with different morphologies (e.g., particles, nanotubes, and nanowires) were successfully prepared by adding or without adding different kinds of surfactants through a chemical oxidative polymerization method, respectively. The results show that the morphologies of PPy can be effectively controlled and have a significantly effects on their thermoelectric properties. The PPy nanowires exhibit the highest electrical conductivity and Seebeck coefficient among the various PPy morphologies, such as particles, nanotubes, and nanowires, so PPy nanowires were chosen to prepare PPy nanowire/graphene thermoelectric composites via a soft template polymerization method using cetyltrimethyl ammonium bromide as the template. Both electrical conductivity and Seebeck coefficient of the PPy nanowire/graphene composites increased as the content of graphene increases from 0 to 20 wt %, and as the measured temperature increases from 300 K to 380 K, which leds to the same trend for the power factor. A highest power factor of 1.01 μWm−1K−2 at ~380 K was obtained for the PPy nanowire/graphene composites with 20 wt % PPy nanowire, which is about 3.3 times higher than that of the pure PPy nanowire.
Thermoelectric materials with the thermoelectric figure of merit, ZT, being much larger than unit at near room temperature are vital for power generation by using low-grade waste heat. Here we show that by incorporating very small proportion (1 vol%) of Cu 3 SbSe 4 nanoparticles into the BiSbTe matrix to form nanocomposites, besides large (B50%) reduction of lattice thermal conductivity, both enhanced thermopower through energy-dependent scattering and alleviated reduction of carrier mobility via carrier scattering at heterojunction potentials occur at elevated temperatures, which allow the thermoelectric power factor of the composite material to reach B37 mW cm À1 K À2 at 467 K. Consequently, a largest value of ZT = 1.6 is achieved at 476 K. Moreover, it has excellent performance in a broad temperature range (say, ZT = 1.0 at 300 K and ZT = 1.5 at 500 K), which makes this material attractive for cooling and power generation.
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