Scattering Mechanisms and Suppression of Bipolar Diffusion Effect in Bi2Te2.85Se0.15Ix Compounds

Abstract

We investigated the anisotropic thermoelectric properties of the Bi2Te2.85Se0.15Ix (x = 0.0, 0.1, 0.3, 0.5 mol.%) compounds, synthesized by ball-milling and hot-press sintering. The electrical conductivities of the Bi2Te2.85Se0.15Ix were significantly improved by the increase of carrier concentration. The dominant electronic scattering mechanism was changed from the mixed (T ≤ 400 K) and ionization scattering (T ≥ 420 K) for pristine compound (x = 0.0) to the acoustic phonon scattering by the iodine doping. The Hall mobility was also enhanced with the increasing carrier concentration. The enhancement of Hall mobility was caused by the increase of the mean free path of the carrier from 10.8 to 17.7 nm by iodine doping, which was attributed to the reduction of point defects without the meaningful change of bandgap energy. From the electron diffraction patterns, a lattice distortion was observed in the iodine doped compounds. The modulation vector due to lattice distortion increased with increasing iodine concentration, indicating the shorter range lattice distortion in real space for the higher iodine concentration. The bipolar thermal conductivity was suppressed, and the effective masses were increased by iodine doping. It suggests that the iodine doping minimizes the ionization scattering giving rise to the suppression of the bipolar diffusion effect, due to the prohibition of the BiTe1 antisite defect, and induces the lattice distortion which decreases lattice thermal conductivity, resulting in the enhancement of thermoelectric performance.

Ultralow Lattice Thermal Conductivity and Improved Thermoelectric Performance in Cl-Doped Bi2Te3–xSex Alloys

“…Particularly, Cl-doped samples show higher carrier mobility compared with the undoped sample (Table ). A similar phenomenon was also observed for I-doped Bi 2 Te 3– x Se x materials by Kim et al and Hong et al While Hong et al did not highlight the reason for the enhanced mobility by halogen doping, Kim et al connected this effect with the larger mean free path of the carriers due to reduction point defects in halogen-doped Bi 2 Te 3– x Se x materials. Let us discuss this effect in more detail for the case of Cl-doped Bi 2 Te 3– x Se x .…”

“…Chlorine as a doping element in Bi 2 Te 3– x Se x alloys was chosen due to the following reasons. Halogen atoms (iodine, chlorine, and bromine) in the investigated alloys are known to be donor impurities. − The number of electrons in the valence shell of halogen atoms is one more than that in tellurium atoms; therefore, a halogen atom can donate one electron to the conduction band. Moreover, the interaction of this electron with the ionized halogen atom will be weakened due to the strong influence of the polarization of media as a result of the high dielectric constant (ε = 80); hence, the negative effect of halogen doping on the carrier mobility μ should not be significant.…”

Thermoelectric Properties of Single-Phase n-Type Bi14Te13S8

“…This is due to very low concentration of the iodine dopant and small differences in ionic radii of S 2– (0.184 nm) and Te 2– (0.221 nm) with I 1– (0.22 nm) . Similar behavior was observed in iodine-doped Bi 2 Te 3 . , The obtained lattice parameters are consistent with literature-reported values of a = b = 1.1269 nm and c = 1.1129 nm…”

Achieving high thermoelectric conversion efficiency in Bi2Te3-based stepwise legs through bandgap tuning and chemical potential engineering

“…In this work, we used Cl, which has been recently reported as a promising halogen dopant in Bi 2 Te 3−x Se x alloys for high thermoelectric performance. 30,35 The increased bandgap and deeper position of the chemical potential of electrons give the possibility of shifting the ZT parameter towards higher temperatures, which is in line with the stepwise leg approach.…”