Microstructure engineering is an effective strategy to reduce lattice thermal conductivity (κl) and enhance the thermoelectric figure of merit (
Bismuth telluride is the working material for most Peltier cooling devices and thermoelectric generators. This is because Bi2Te3(or more precisely its alloys with Sb2Te3for p‐type and Bi2Se3for n‐type material) has the highest thermoelectric figure of merit,
- NSF-PAR ID:
- 10461107
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Electronic Materials
- Volume:
- 5
- Issue:
- 6
- ISSN:
- 2199-160X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract zT ). Through a new process based on melt‐centrifugation to squeeze out excess eutectic liquid, microstructure modulation is realized to manipulate the formation of dislocations and clean grain boundaries, resulting in a porous network with a platelet structure. In this way, phonon transport is strongly disrupted by a combination of porosity, pore surfaces/junctions, grain boundaries, and lattice dislocations. These collectively result in a ≈60% reduction of κlcompared to zone melted ingot, while the charge carriers remain relatively mobile across the liquid‐fused grains. This porous material displays azT value of 1.2, which is higher than fully dense conventional zone melted ingots and hot pressed (Bi,Sb)2Te3alloys. A segmented leg of melt‐centrifuged Bi0.5Sb1.5Te3and Bi0.3Sb1.7Te3could produce a high deviceZT exceeding 1.0 over the whole temperature range of 323–523 K and an efficiency up to 9%. The present work demonstrates a method for synthesizing high‐efficiency porous thermoelectric materials through an unconventional melt‐centrifugation technique. -
Abstract PbSe is an attractive thermoelectric material due to its favorable electronic structure, high melting point, and lower cost compared to PbTe. Herein, the hitherto unexplored alloys of PbSe with NaSbSe2(NaPb
m SbSem +2) are described and the most promising p‐type PbSe‐based thermoelectrics are found among them. Surprisingly, it is observed that below 500 K, NaPbm SbSem +2exhibits unorthodox semiconducting‐like electrical conductivity, despite possessing degenerate carrier densities of ≈1020cm−3. It is shown that the peculiar behavior derives from carrier scattering by the grain boundaries. It is further demonstrated that the high solubility of NaSbSe2in PbSe augments both the thermoelectric properties while maintaining a rock salt structure. Namely, density functional theory calculations and photoemission spectroscopy demonstrate that introduction of NaSbSe2lowers the energy separation between the L‐ and Σ‐valence bands and enhances the power factors under 700 K. The crystallographic disorder of Na+, Pb2+, and Sb3+moreover provides exceptionally strong point defect phonon scattering yielding low lattice thermal conductivities of 1–0.55 W m‐1K‐1between 400 and 873 K without nanostructures. As a consequence, NaPb10SbSe12achieves maximumZT ≈1.4 near 900 K when optimally doped. More importantly, NaPb10SbSe12maintains highZT across a broad temperature range, giving an estimated recordZT avgof ≈0.64 between 400 and 873 K, a significant improvement over existing p‐type PbSe thermoelectrics. -
Abstract Sb‐doped and GeTe‐alloyed n‐type thermoelectric materials that show an excellent figure of merit
ZT in the intermediate temperature range (400–800 K) are reported. The synergistic effect of favorable changes to the band structure resulting in high Seebeck coefficient and enhanced phonon scattering by point defects and nanoscale precipitates resulting in reduction of thermal conductivity are demonstrated. The samples can be tuned as single‐phase solid solution (SS) or two‐phase system with nanoscale precipitates (Nano) based on the annealing processes. The GeTe alloying results in band structure modification by widening the bandgap and increasing the density‐of‐states effective mass of PbTe, resulting in significantly enhanced Seebeck coefficients. The nanoscale precipitates can improve the power factor in the low temperature range and further reduce the lattice thermal conductivity (κlat). Specifically, the Seebeck coefficient of Pb0.988Sb0.012Te–13%GeTe–Nano approaches −280 µV K−1at 673 K with a low κlatof 0.56 W m−1K−1at 573 K. Consequently, a peakZT value of 1.38 is achieved at 623 K. Moreover, a high averageZT avgvalue of ≈1.04 is obtained in the temperature range from 300 to 773 K for n‐type Pb0.988Sb0.012Te–13%GeTe–Nano. -
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