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Abstract Cation substitutional doping has been shown to be an effective method to modify both the electronic and thermal transport in p -type (Bi,Sb) 2 Te 3 -based thermoelectric alloys. However, there are not many studies that have attempted a quantitative analysis on the influence of cation substitution on the electronic and thermal properties of n -type Bi 2 (Te,Se) 3 -based alloys. In this work, we report a comprehensive analysis of the influence of substitutional Nb doping on the electrical and thermal conductivity in n -type Cu 0.008 Bi 2 Te 2.7 Se 0.3 alloys. First, we found that Nb doping increases the carrier concentration of both the electrons and holes, whereas the weighted mobility of the electrons and holes is only slightly modified based on a single parabolic band model. As a result, the bipolar thermal conductivity was increased as the Nb was doped. Next, the contribution of point defect scattering by the Nb substitution on the thermal conductivity of the lattice was quantitatively analyzed using a Debye-Callaway model, and it was concluded that the influence of cation substitutional doping in n -type Bi 2 (Te,Se) 3 is as effective as that in p -type (Bi,Sb) 2 Te 3. Highlights • Electronic properties of Nb-doped n -type Cu 0.008 Bi 2 Te 2.7 Se 0.3 alloys was analyzed. • Carrier concentrations of electrons and holes were increased by the Nb doping. • Reduction of lattice thermal conductivities was analyzed based on Callaway model. • Doping in n -type Cu-Bi 2 Te 2.7 Se 0.3 is effective in reducing thermal conductivity. [ABSTRACT FROM AUTHOR]

Substitutional doping is known to be effective when used to enhance the thermoelectric figure of merit zT , and this is generally explained as resulting from a reduction in the thermal conductivity caused by an additional atomic-scale defect structure. However, a comprehensive analysis of the substitutional doping effect on the electrical and thermal properties together has not been undertaken, especially when the bipolar thermal conductivity becomes serious. A previous study by the authors also showed that the zT of Bi 0.4 Sb 1.6 Te 3 thermoelectric alloys was enhanced by indium (In) doping due to the reduction of the total thermal conductivity. Here, we more closely analyze the electrical and thermal transport properties of a series of indium (In)-doped p-type Bi 0.4 Sb 1.6-x In x Te 3 (x = 0, 0.003, 0.005, 0.01) using both the single-parabolic-band model and the Debye-Callaway model in an effort to investigate the origin of the observed thermal conductivity reduction more closely. The bipolar contribution to the total thermal conductivity was estimated exclusively based on a two-band model based on a single-parabolic-band model. Furthermore, the lattice thermal conductivity was calculated using the Debye-Callaway model while taking additional In substitutional defects into consideration. The calculations indicated that the significant suppression of bipolar thermal conductivity was achieved as a result of the increased bandgap in Bi 0.4 Sb 1.6 Te 3 caused by In doping. Additional point defects from In doping also reduced the lattice thermal conductivity, but not as much as the bipolar thermal conductivity did. The study suggests that the suppression of bipolar conduction by means of a bandgap modification can be an effective approach for enhancing zT further via a simple In-doping process in Bi 0.4 Sb 1.6 Te 3 . [ABSTRACT FROM AUTHOR]

A unique method taking advantage of a synergistic effect at (LaVO 3)/Cu 0.07 Bi 0.5 Sb 1.5 Te 3 interfaces to boost the thermoelectric figure of merit is demonstrated. The unusual electrical conductivity and energy filtering effect largely help to improve power factor and reduce thermal conductivity of the composites. As a result, a high ZT of 1.26 and ZT avg of 1.13 are successfully achieved. [Display omitted] • Mott insulator LaVO 3 (LVO) was added into Cu 0.07 Bi 0.5 Sb 1.5 Te 3 (BST) to boost the ZT. • LVO/BST interface produces an unusual high σ and enhanced energy filtering effect. • Addition of LVO helps to reduce both the bipolar and lattice thermal conductivity. • A high ZT of 1.26 and ZT avg of 1.13 are successfully achieved. • Mechanical properties of the composites are greatly enhanced by the addition of LVO. The enhancement of thermoelectric (TE) figure of merit, ZT, is of great essence to improve the efficiency of TE devices since the commercial applications of TE devices have been constrained due to low performance. Here, we report a novel approach for ZT improvement via a synergistic effect of unusual conducting behavior and energy filtering at the (LaVO 3)/Cu 0.07 Bi 0.5 Sb 1.5 Te 3 incoherent interfaces. In this work, the incoherent interfaces have been engendered by the incorporation of LaVO 3 (LVO) nanoparticles into Cu 0.07 Bi 0.5 Sb 1.5 Te 3 (BST) matrix, inducing a remarkable enhancement in electrical conductivity due to defect formations and an insulator-to-metal transition. This induced conducting behavior also eminently suppressed the adverse intrinsic excitation thanks to increases in hole density and band turning in composites. Meanwhile, the low-work function in the BST matrix establishes an interface potential with a height of 2.03 eV that efficiently filters low energy carriers, and consequently alleviates the decrement of Seebeck coefficients. Upon LVO addition, not only does the bipolar thermal conductivity decrease but the lattice thermal conductivity approaches the amorphous limit due to enhanced phonon scattering mechanisms at incoherent interfaces. A significant thermoelectric figure of merit, ZT of 1.26 and ZT avg = 1.13 are achieved for the sample with 5 wt% of LVO in BST, which is about 26% and 20% higher than the pristine BST, respectively, thanks to its optimized power factor and low thermal conductivity. Additionally, LVO dispersion strengthens the mechanical properties of the composites, demonstrated in their enhanced hardness and compressive strength. [ABSTRACT FROM AUTHOR]

Doping is known as an effective way to modify both electrical and thermal transport properties of thermoelectric alloys to enhance their energy conversion efficiency. In this project, we report the effect of Pd doping on the electrical and thermal properties of n-type Cu0.008Bi2Te2.7Se0.3 alloys. Pd doping was found to increase the electrical conductivity along with the electron carrier concentration. As a result, the effective mass and power factors also increased upon the Pd doping. While the bipolar thermal conductivity was reduced with the Pd doping due to the increased carrier concentration, the contribution of Pd to point defect phonon scattering on the lattice thermal conductivity was found to be very small. Consequently, Pd doping resulted in an enhanced thermoelectric figure of merit, zT, at a high temperature, due to the enhanced power factor and the reduced bipolar thermal conductivity. [ABSTRACT FROM AUTHOR]