Enhanced thermopower and thermoelectric performance through energy filtering of carriers in (Bi2Te3)0.2(Sb2Te3)0.8 bulk alloy embedded with amorphous SiO2 nanoparticles

Abstract

(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.