Multiple Roles of Unconventional Heteroatom Dopants in Chalcogenide Thermoelectrics: The Influence of Nb on Transport and Defects in Bi<sub>2</sub>Te<sub>3</sub>

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Polycrystalline BiCuSeO is considered as a promising thermoelectric material due to its intrinsically low thermal conductivity and moderate Seebeck coefficient. However, its low electrical conductivity and coupled electron−phonon transport properties restrict the further improvement of the thermoelectric performance. In this work, Pb and Yb dopants are incorporated into BiCuSeO to substitute for Bi sites via ball milling and high-pressure and high-temperature sintering, leading to a synergistic optimization of the electron and phonon transport and improved thermoelectric performance. The carrier concentration exhibits an enhancement with increasing Pb&Yb co-doping contents. Meanwhile, the decreased carrier mobility is suppressed appropriately by coordinating with the interplay of Pb and Yb dopants on the electronic structure. Besides, Pb&Yb co-doping combined with high-pressure and high-temperature sintering introduces abundant grain boundaries, dislocations, and point defects to effectively decrease the lattice thermal conductivity by scattering phonons in a broad frequency range. Coupled with the synergistic optimization of the electrical and thermal properties, a maximum zT of 1.2 is achieved in Bi 0.88 Pb 0.06 Yb 0.06 CuSeO at 850 K, which significantly outperforms the majority of oxygen-containing thermoelectric materials. Our study suggests that dual doping of bivalent ions and rare-earth elements at Bi sites is an effective strategy for improving the thermoelectric performance of BiCuSeO.

Section: Resultssupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Synergistically Optimized Electron and Phonon Transport of Polycrystalline BiCuSeO via Pb and Yb Co-Doping

Yin

Liu

et al. 2021

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“…Bi 2 Te 3 -based materials are the most common commercial thermoelectric materials used for thermoelectric refrigeration and also display a typical lamellar structure with a van der Waals gap between Te–Te atoms in the c -axis. The widespread preparation technologies for polycrystalline Bi 2 Te 3 bulks are ball milling, − hot press, hot deformation, chemical synthesis, − and melt spinning; − all these methods lead to nanometer grain size and intense scattering of phonons. Benefiting from the reduced lattice thermal conductivity, the zT values of p-type Bi 2 Te 3 alloys are elevated to more than 1, but the same methods are invalid for n-type Bi 2 Te 3 alloys due to the severe deterioration of electron mobility caused by sensitive anisotropy .…”

Section: Introductionmentioning

confidence: 99%

Isotropic Thermoelectric Performance of Layer-Structured n-Type Bi₂Te_2.7Se_0.3 by Cu Doping

Chen

Shi

et al. 2021

The lamellar structure of (Bi,Sb) 2 (Te,Se) 3 alloys makes it difficult to achieve isotropic thermoelectric properties in the directions along and perpendicular to the c-axis, especially for n-type samples. In this work, by introducing Cu in polycrystalline ntype Cu x Bi 2 Te 2.7 Se 0.3 and applying the traditional synthesis process of high-energy ball milling and hot pressing, substantial enhancement of the thermoelectric figure of merit zT is obtained in both in-plane and out-of-plane directions. The intercalated Cu not only provides electron transport media for mobility improvement but also reduces the lattice thermal conductivity owing to the strain fluctuation. Typically, the van der Waals gap in the out-of-plane direction leads to relatively slower mobility and lower lattice thermal conductivity. Taking into account the same average density-of-state effective mass (m avg * ∼ 1.5m e ) predicted based on a single parabolic model, the obtained quality factor β is comparable in both directions. As a result, a peak zT ∼ 1.05 at 420 K and the average zT approaching to 1.0 in the temperature range 300−500 K are obtained in both directions for the Cu 0. 02 Bi 2 Te 2.7 Se 0.3 sample. The simple synthesis process and isotropic thermoelectric properties in this work make n-type Bi 2 Te 3 more convenient for potential production and application. KEYWORDS: n-type Bi 2 Te 2.7 Se 0.3 , isotropic, Cu doping, quality factor, thermoelectric

“…It is also worth noting that the improvement in the average ZT of the material over the working temperature range is more important than that in the peak ZT value at a certain temperature concerning the operation efficiency of the thermoelectric device in practice. − To date, tremendous investigations have demonstrated that the effective approaches to maximize the ZT value can be categorized by boosting electrical transport properties and/or decreasing thermal conductivity. The methods to boost the power factor include appropriate levels of doping to optimize carrier concentration, the introduction of unique defect structures, electronic band structure engineering, etc. − Meanwhile, nanostructuring, the formation of solid solution, and all-length-scale hierarchical architectures have pronounced great effectiveness in lowering the thermal conductivity. − So far, considerable efforts based on the above strategies have been made toward achieving high thermoelectric performance in the existing thermoelectric materials, including (Bi, Sb) 2 Te 3 alloys, − PbTe-based compounds, − and SnTe-based materials. − …”

Section: Introductionmentioning

confidence: 99%

Zn-Induced Defect Complexity for the High Thermoelectric Performance of n-Type PbTe Compounds

Cao

Bai

et al. 2021

Although defect engineering is the core strategy to improve thermoelectric properties, there are limited methods to effectively modulate the designed defects. Herein, we demonstrate that a high ZT value of 1.36 at 775 K and a high average ZT value of 0.99 in the temperature range from 300 to 825 K are realized in Zn-containing PbTe by designing complex defects. By combining first-principles calculations and experiments, we show that Zn atoms occupy both Pb sites and interstitial sites in PbTe and couple with each other. The contraction stress induced via substitutional Zn on Pb sites alleviates the swelling stress by Zn atoms occupying the interstitial sites and promotes the solubility of interstitial Zn atoms in the structure of PbTe. The stabilization of Zn impurity as a complex defect extends the region of PbTe phase stability toward Pb0.995Zn0.02Te, while the solid solution region in the other direction of the ternary phase diagram is much smaller. The evolution of defects in PbTe was further explicitly corroborated by aberration-corrected scanning transmission electron microscopy (Cs-corrected STEM) and positron annihilation measurement. The Zn atoms compensate the Pb vacancies (VPb) and Zn interstitials (Zni) significantly improve the electron concentration, producing a high carrier mobility of 1467.7 cm2 V–1 s–1 for the Pb0.995Zn0.02Te sample. A high power factor of 4.11 mW m–1 K–2 is achieved for the Pb0.995Zn0.02Te sample at 306 K. This work provides new insights into understanding the nature and evolution of the defects in n-type PbTe as well as improving the electronic and thermal transport properties toward higher thermoelectric performance.