Abstract
In order to understand the effect of Pb-CuI co-doping on the thermoelectric performance of Bi2Te3, n-type Bi2Te3 co-doped with x at % CuI and 1/2x at % Pb (x = 0, 0.01, 0.03, 0.05, 0.07, and 0.10) were prepared via high temperature solid state reaction and consolidated using spark plasma sintering. Electron and thermal transport properties, i.e., electrical conductivity, carrier concentration, Hall mobility, Seebeck coefficient, and thermal conductivity, of CuI-Pb co-doped Bi2Te3 were measured in the temperature range from 300 K to 523 K, and compared to corresponding x% of CuI-doped Bi2Te3 and undoped Bi2Te3. The addition of a small amount of Pb significantly decreased the carrier concentration, which could be attributed to the holes from Pb atoms, thus the CuI-Pb co-doped samples show a lower electrical conductivity and a higher Seebeck coefficient when compared to CuI-doped samples with similar x values. The incorporation of Pb into CuI-doped Bi2Te3 rarely changed the power factor because of the trade-off relationship between the electrical conductivity and the Seebeck coefficient. The total thermal conductivity(κtot) of co-doped samples (κtot ~ 1.4 W/m∙K at 300 K) is slightly lower than that of 1% CuI-doped Bi2Te3 (κtot ~ 1.5 W/m∙K at 300 K) and undoped Bi2Te3 (κtot ~ 1.6 W/m∙K at 300 K) due to the alloy scattering. The 1% CuI-Pb co-doped Bi2Te3 sample shows the highest ZT value of 0.96 at 370 K. All data on electrical and thermal transport properties suggest that the thermoelectric properties of Bi2Te3 and its operating temperature can be controlled by co-doping.
Highlights
Bismuth telluride (Bi2 Te3 ) has been the focus of extensive theoretical and experimental studies as a component of materials for thermoelectric (TE) devices, such as solid-state coolers or generators [1,2,3].The performance of a thermoelectric material in the aforementioned applications is evaluated in terms of a dimensionless figure of merit ZT, which is defined as (S2 σ/κ)T; where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the temperature [4]
All of the diffraction peaks are indexed to rhombohedral Bi2 Te3 structure with the space group of R3m (JCPDS, No 15-0863) [21], with no indication for the existence of a second phase for samples with up to 7% of dopant concentration
Trace amounts of possible impurities including Cu2−x Te, and CuI were detected in the 10% CuI-Pb co-doped Bi2 Te3 samples
Summary
Bismuth telluride (Bi2 Te3 ) has been the focus of extensive theoretical and experimental studies as a component of materials for thermoelectric (TE) devices, such as solid-state coolers or generators [1,2,3]. The poor performance of n-type Bi2 Te3 based materials compared to that of p-type materials seriously inflicts a limitation on making it a more efficient TE device. Both p-type and n-type characteristics of Bi2 Te3 can be controlled depending on the chemical composition. The addition of dopant atoms at Bi sites in n-type Cu-intercalated Bi2 Te3 changes the electronic band structure, such as band position and band degeneracies, resulting in an increase of the Seebeck coefficient. It has great potential to further improve the ZT value of n-type Bi2 Te3 based materials via compositional tuning approach by adjusting Cu contents or element doping.
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