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Herein, we report a reproducible improvement of the thermoelectric performance in BiSbTe alloy via kinetically and dynamically regulating excitation behavior in the intrinsic excitation regime. Doping with Pb increases the carrier concentration to the optimal value, kinetically pushing the onset temperature for the intrinsic excitation from 350 K for Bi0.46Sb1.54Te3 sample to 450 K for Pb0.01(Bi0.46Sb1.54)0.995Te3 sample. Moreover, the refined grains, nanostructures as well as dense dislocations induced by the melt-spinning process not only lower the lattice thermal conductivity via intensifying the interfacial phonon scattering but also selectively block the migration of minority carrier, modifying the dynamic process of the charge carrier and resulting in a smaller ratio of ( μ e / μ h ). This improves the power factor in the measured temperature range and suppresses the bipolar thermal conductivity in the intrinsic excitation regime. Thus, a maximum power factor of 4.44 mW m−1 K−2 and the lowest thermal conductivity of 1.06 W m−1 K−1 are attained for the sample with refined grains and nanostructures. All these contribute to the highest ZT value of 1.31 at 380 K and the highest average ZT value of 1.17 from 300 K to 500 K for Pb0.002(Bi0.46Sb1.54)0.999Te3 sample. This improved thermoelectric property was further verified in a thermoelectric module with the conversion efficiency of 4.38 % under a temperature gradient of 175 K, which is 20 % higher than that of the commercial ZM-based module under the same temperature gradient.

Cd-containing polycrystalline Bi0.46Sb1.54Te3 samples with precisely controlled phase composition were synthesized by conventional melting-quenching-annealing technique and a melt-spinning method. ...

Bismuth telluride-based alloys are the best performing thermoelectric materials near room temperature. Grain size refinement and nanostructuring are the core stratagems for improving thermoelectric and mechanical properties. However, the donor-like effect induced by grain size refinement strongly restricts the thermoelectric properties especially in the vicinity of room temperature. In this study, the formation mechanism for the donor-like effect in Bi

Cd-containing polycrystalline Bi

In this study, a series of Bi2Te2-xS1+x compounds were prepared by traditional melting-quenching-annealing process. In the range of 0.03 ≤ x ≤ 0.25, Bi2Te2-xS1+x compounds possess the Bi2Te3 structure. S atoms preferentially fully occupy the Te(2) sites, while any extra S atoms randomly occupy the Te(1) sites. Experimental results and phonon dispersion calculations demonstrate that the strong coupling of the phonon density of state contributed by Bi and Te(1) atoms results in the low avoided-crossing frequencies, sound velocities, Debye temperature and therefore the low lattice thermal conductivities. Moreover, substitutions of extra S atoms on the Te(1) site intensifies alloy phonon scattering that further suppresses the lattice thermal conductivity. An ultra-low lattice thermal conductivity of 0.49 W m−1 K−1 is achieved at 523 K. Doping with Cl increases the room temperature carrier concentration, resulting in a significantly enhanced power factor from 1.5 mW m−1 K−2 for the Bi2Te1.93S1.07 sample to 1.7 mW m−1 K−2 for the Cl-doped sample at 323 K. Furthermore, doping with Cl enhances phonon point defect scattering that leads to a suppression of the thermal conductivity to 0.41 W m−1 K−1 at 573 K. As a result of the optimization of the electronic transport properties and the reduction in the lattice thermal conductivity, Bi2Te1.93S1.065Cl0.005 sample achieved the highest ZT of 0.67 at 623 K which is superior to intrinsic Bi2Te3 in the whole temperature range.

Bi2Te3 films always exhibit n-type transport characteristics even under the Bi-rich condition, which, however, was not clarified clearly. Herein, by virtue of advanced techniques such as scanning tunneling microscopy, angle-resolved photoelectron spectroscopy, scanning transmission electron microscopy, and x-ray photoelectron spectroscopy, we are able to identify the structural evolution on the atomic scale for Bi-rich Bi2Te3 films. The excess of Bi content will lead to the formation of p-type BiTe antisite defects; however, there is a doping limit for the excess of Bi to form BiTe antisites. Beyond this limit, the excess of Bi will form the n-type Bi2 planar defects in the van der Waals gap, the excellent electron donors, which can enhance the electron density by over one order of magnitude and up to the 1021 cm−3 range for Bi-rich Bi2Te3 films. Benefiting from the remarkable increase in the electron density and the suppression of carrier intrinsic excitations, Bi2Te3 films with Bi2 planar defects possess a much improved thermoelectric power factor, with a maximum value of 1.4 mW m−1 K−2 at 450 K, showing about 130% enhancement compared to that of the film without Bi2 intercalations. The discovery opens a new avenue to improve the thermoelectric properties of Bi2Te3 films utilizing the Bi2 planar defects.

Herein, the influence of Sn and Ge doping on the structure and thermoelectric properties of p-type Bi2Te3-based thermoelectric materials is systematically studied. Sn and Ge exhibit distinct doping characteristics in Bi2Te3-based thermoelectric materials. Doping with Sn in BiSbTe alloy not only increases the carrier concentration but also induces resonant electronic states, greatly improving the Seebeck coefficient and power factor. A maximum power factor of 3.8 ​mWm−1K−2 ​at 320 ​K is attained for Sn0.002(Bi0.46Sb1.54)0.999Te3 sample. In contrast, doping with Ge augments the carrier concentration very rapidly, resulting in a large deviation from the optimum carrier concentration (2 ​× ​1019–2.5 ​× ​1019 ​cm−3). Thus, the increase in the electrical conductivity is cancelled out by the reduced Seebeck coefficient, producing an almost unchanged power factor of 3.5 ​mWm−1K−2 ​at room temperature. The enhanced electrical conductivity via doping with Sn or Ge increases the total thermal conductivity slightly and suppresses the bipolar thermal conductivity. Because of the significantly improved power factor and lower thermal conductivity in Sn doping samples, the maximum ZT value of 1.02 ​at 345 ​K is obtained for the sample with Sn doping of 0.002, which is 12% higher than that of the pristine sample.