22 results on '"Dravid, Vinayak P."'
Search Results
2. Strained endotaxial nanostructures with high thermoelectric figure of merit.
- Author
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Biswas K, He J, Zhang Q, Wang G, Uher C, Dravid VP, and Kanatzidis MG
- Subjects
- Lead chemistry, Manufactured Materials, Sodium chemistry, Strontium chemistry, Tellurium chemistry, Electric Conductivity, Nanoparticles chemistry, Nanostructures chemistry, Thermal Conductivity
- Abstract
Thermoelectric materials can directly generate electrical power from waste heat but the challenge is in designing efficient, stable and inexpensive systems. Nanostructuring in bulk materials dramatically reduces the thermal conductivity but simultaneously increases the charge carrier scattering, which has a detrimental effect on the carrier mobility. We have experimentally achieved concurrent phonon blocking and charge transmitting via the endotaxial placement of nanocrystals in a thermoelectric material host. Endotaxially arranged SrTe nanocrystals at concentrations as low as 2% were incorporated in a PbTe matrix doped with Na(2)Te. This effectively inhibits the heat flow in the system but does not affect the hole mobility, allowing a large power factor to be achieved. The crystallographic alignment of SrTe and PbTe lattices decouples phonon and electron transport and this allows the system to reach a thermoelectric figure of merit of 1.7 at ~800 K.
- Published
- 2011
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3. Weak Electron–Phonon Coupling and Enhanced Thermoelectric Performance in n‐type PbTe–Cu2Se via Dynamic Phase Conversion.
- Author
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Wu, Ming, Cui, Hong‐Hua, Cai, Songting, Hao, Shiqiang, Liu, Yukun, Bailey, Trevor P., Zhang, Yinying, Chen, Zixuan, Luo, Yubo, Uher, Ctirad, Wolverton, Christopher, Dravid, Vinayak P., Yu, Yan, Luo, Zhong‐Zhen, Zou, Zhigang, Yan, Qingyu, and Kanatzidis, Mercouri G.
- Subjects
PHONON scattering ,CARRIER density ,THERMOELECTRIC materials ,ELECTRIC conductivity ,THERMAL conductivity ,DOPING agents (Chemistry) - Abstract
This study investigates Ga‐doped n‐type PbTe thermoelectric materials and the dynamic phase conversion process of the second phases via Cu2Se alloying. Introducing Cu2Se enhances its electrical transport properties while reducing its lattice thermal conductivity (κlat) via weak electron–phonon coupling. Cu2Te and CuGa(Te/Se)2 (tetragonal phase) nanocrystals precipitate during the alloying process, resulting in Te vacancies and interstitial Cu in the PbTe matrix. At room temperature, Te vacancies and interstitial Cu atoms serve as n‐type dopants, increasing the carrier concentration and electrical conductivity from ≈1.18 × 1019 cm−3 and ≈1870 S cm−1 to ≈2.26 × 1019 cm−3 and ≈3029 S cm−1, respectively. With increasing temperature, the sample exhibits a dynamic change in Cu2Te content and the generation of a new phase of CuGa(Te/Se)2 (cubic phase), strengthening the phonon scattering and obtaining an ultralow κlat. Pb0.975Ga0.025Te‐3%CuSe exhibits a maximum figure of merit of ≈1.63 at 823 K, making it promising for intermediate‐temperature device applications. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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4. Ultralow thermal conductivity and high-temperature thermoelectric performance in n-type K₂.₅Bi₈.₅Se₁₄
- Author
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Luo, Zhong-Zhen, Cai, Songting, Hao, Shiqiang, Bailey, Trevor P., Hu, Xiaobing, Hanus, Riley, Ma, Runchu, Tan, Gangjian, Chica. Daniel G., Snyder, G. Jeffrey, Uher, Ctirad, Wolverton, Christopher, Dravid, Vinayak P., Yan, Qingyu, Kanatzidis, Mercouri G., and School of Materials Science and Engineering
- Subjects
Materials::Functional materials [Engineering] ,Phonons ,Thermal Conductivity - Abstract
We studied the narrow bandgap (0.55 eV) semiconductor K2.5Bi8.5Se14, as a potential thermoelectric material for power generation. Samples of polycrystalline K2.5Bi8.5Se14 prepared by spark plasma sintering exhibit exceptionally low lattice thermal conductivities (κlat) of 0.57 − 0.33 Wm−1K−1 in the temperature range of 300 − 873 K. The physical origin of such low κlat in K2.5Bi8.5Se14 is related to the strong anharmonicity and low phonon velocity caused by its complex low-symmetry, large unit cell crystal structure and mixed-occupancy of Bi and K atoms in the lattice. High-resolution scanning transmission electron microscopy (HRSTEM) studies and micro-analysis indicates that the K2.5Bi8.5Se14 sample is a single phase without intergrowth of the structurally related K2Bi8Se13 phase. The undoped material exhibits n-type character and a figure of merit (ZT) value of 0.67 at 873 K. Electronic band structure calculations indicate that K2.5Bi8.5Se14 is an indirect bandgap semiconductor with multiple conduction bands close to the Fermi level. Phonon dispersion calculations suggest K2.5Bi8.5Se14 has low phonon velocities and large Grüneisen parameters that can account for the observed ultralow κlat. The degree of n-type doping can be controlled by introducing Se deficiencies in the structure providing a simple route to increase the ZT to ~1 at 873 K. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) Submitted/Accepted version This work was supported by the Department of Energy, Office of Science Basic Energy Sciences under grant DE-SC0014520, DOE Office of Science (sample preparation, synthesis, XRD, TE measurements, TEM measurements, DFT calculations). Z.-Z.L. and Q.Y. gratefully acknowledge the National Natural Science Foundation of China (61728401). This work made use of the EPIC facility of Northwestern University’s NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), the MRSEC program (NSF DMR1720139) at the Materials Research Center, the International Institute for Nanotechnology (IIN), the Keck Foundation, and the State of Illinois, through the IIN. User Facilities are supported by the Office of Science of the U.S. Department of Energy under Contract Nos. DE-AC02-06CH11357 and DEAC02-05CH11231. Access to facilities of high-performance computational resources at Northwestern University is acknowledged. The authors also acknowledge Singapore MOE AcRF Tier 2 under Grant Nos. 2018-T2-1-010 and MOE2017-T2-2-069, Singapore A*STAR Pharos Program SERC 1527200022, and the support from FACTs of Nanyang Technological University for sample analysis.
- Published
- 2019
5. Strong Valence Band Convergence to Enhance Thermoelectric Performance in PbSe with Two Chemically Independent Controls.
- Author
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Luo, Zhong‐Zhen, Cai, Songting, Hao, Shiqiang, Bailey, Trevor P., Spanopoulos, Ioannis, Luo, Yubo, Xu, Jianwei, Uher, Ctirad, Wolverton, Christopher, Dravid, Vinayak P., Yan, Qingyu, and Kanatzidis, Mercouri G.
- Subjects
VALENCE bands ,ELECTRONIC structure ,POINT defects ,THERMAL conductivity ,ENERGY bands - Abstract
We present an effective approach to favorably modify the electronic structure of PbSe using Ag doping coupled with SrSe or BaSe alloying. The Ag 4d states make a contribution to in the top of the heavy hole valence band and raise its energy. The Sr and Ba atoms diminish the contribution of Pb 6s2 states and decrease the energy of the light hole valence band. This electronic structure modification increases the density‐of‐states effective mass, and strongly enhances the thermoelectric performance. Moreover, the Ag‐rich nanoscale precipitates, discordant Ag atoms, and Pb/Sr, Pb/Ba point defects in the PbSe matrix work together to reduce the lattice thermal conductivity, resulting a record high average ZTavg of around 0.86 over 400–923 K. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
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6. High thermoelectric figure of merit and improved mechanical properties in melt quenched PbTe–Ge and PbTe–Ge1-xSix eutectic and hypereutectic composites.
- Author
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Sootsman, Joseph R., He, Jiaqing, Dravid, Vinayak P., Li, Chang-Peng, Uher, Ctirad, and Kanatzidis, Mercouri G.
- Subjects
THERMOELECTRICITY ,MECHANICAL behavior of materials ,EUTECTIC alloys ,MICROSTRUCTURE ,BRITTLENESS ,THERMOELECTRIC materials ,THERMAL conductivity - Abstract
We report the synthesis, microstructure, and transport properties of composite thermoelectric materials based on the eutectic phase relationship between PbTe and Ge. When quenched, these eutectic mixtures exhibit considerably stronger mechanical strength and reduced brittleness compared to PbTe itself, while at the same time they possess lower lattice thermal conductivity. Thermal conductivity measurements show values lower than expected based on the law of mixtures and multiphase composites. We find that the thermoelectric performance in these composites can be tuned through the use of hypereutectic compositions and alloying of Ge with Si. PbI
2 was used as an n-type dopant, and precise control of the carrier concentration was achieved to optimize the electrical transport and thermoelectric properties. ZT values approaching 1.3 at 778 K have been obtained in samples of PbTe–Ge0.8 Si0.2 (5%), which represent an ∼62% improvement over that of PbTe. [ABSTRACT FROM AUTHOR]- Published
- 2009
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7. High Thermoelectric Performance in Supersaturated Solid Solutions and Nanostructured n‐Type PbTe–GeTe.
- Author
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Luo, Zhong‐Zhen, Zhang, Xiaomi, Hua, Xia, Tan, Gangjian, Bailey, Trevor P., Xu, Jianwei, Uher, Ctirad, Wolverton, Chris, Dravid, Vinayak P., Yan, Qingyu, and Kanatzidis, Mercouri G.
- Subjects
THERMOELECTRICITY ,NANOSTRUCTURED materials ,THERMOELECTRIC materials ,PHONON scattering ,THERMAL conductivity measurement - Abstract
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 (κ
lat ). Specifically, the Seebeck coefficient of Pb0.988 Sb0.012 Te–13%GeTe–Nano approaches −280 µV K−1 at 673 K with a low κlat of 0.56 W m−1 K−1 at 573 K. Consequently, a peak ZT value of 1.38 is achieved at 623 K. Moreover, a high average ZTavg value of ≈1.04 is obtained in the temperature range from 300 to 773 K for n‐type Pb0.988 Sb0.012 Te–13%GeTe–Nano. [ABSTRACT FROM AUTHOR]- Published
- 2018
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8. Large‐Scale Fabrication of MoS2 Ribbons and Their Light‐Induced Electronic/Thermal Properties: Dichotomies in the Structural and Defect Engineering.
- Author
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Li, Yuan, Moy, Emily C., Murthy, Akshay A., Hao, Shiqiang, Cain, Jeffrey D., Hanson, Eve D., DiStefano, Jennifer G., Chae, Woo Hyun, Li, Qianqian, Wolverton, Chris, Chen, Xinqi, and Dravid, Vinayak P.
- Subjects
MOLYBDENUM disulfide ,ELECTROCHEMISTRY ,THERMAL properties ,PHOTOTRANSISTORS ,SEMICONDUCTORS - Abstract
Abstract: Controlled design and patterning of layered transition metal dichalcogenides (TMDs) into specific dimensions and geometries hold great potential for next‐generation micro/nanoscale electronic applications. Herein, the large‐scale fabrication of MoS
2 ribbons with widths ranging from micro‐ to nanoscale is reported. Their unique electric and thermal properties introduced by the shape change and defect creation are also demonstrated, with particular focus on the performance associated with light–matter interactions. The theoretical calculation indicates significantly increased absorption and scattering efficiency of the MoS2 ribbons with decreasing width. As a result, enhanced photocarrier generation ability is detected on their phototransistors with defect‐modulated light‐response behavior. The light‐induced thermal transport properties of the MoS2 ribbons are further studied. A decreased thermal conductivity is observed on narrower ribbons, attributed to the defects created during fabrication. It is also found that the effect of phonon scattering at ribbon edges on their thermal conductivity is insignificant, and the thermal transport has no obvious dependence on the ribbon direction at such width scale. This study evaluates the prospects for designing and fabricating TMD semiconductors with specific geometries for future optoelectronic applications. [ABSTRACT FROM AUTHOR]- Published
- 2018
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9. Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals.
- Author
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Zhao, Li-Dong, Lo, Shih-Han, Zhang, Yongsheng, Sun, Hui, Tan, Gangjian, Uher, Ctirad, Wolverton, C., Dravid, Vinayak P., and Kanatzidis, Mercouri G.
- Subjects
THERMAL conductivity ,THERMOELECTRIC effects ,ELECTRICAL energy ,WASTE heat ,TIN compounds ,CRYSTALS - Abstract
The thermoelectric effect enables direct and reversible conversion between thermal and electrical energy, and provides a viable route for power generation from waste heat. The efficiency of thermoelectric materials is dictated by the dimensionless figure of merit, ZT (where Z is the figure of merit and T is absolute temperature), which governs the Carnot efficiency for heat conversion. Enhancements above the generally high threshold value of 2.5 have important implications for commercial deployment, especially for compounds free of Pb and Te. Here we report an unprecedented ZT of 2.6 ± 0.3 at 923 K, realized in SnSe single crystals measured along the b axis of the room-temperature orthorhombic unit cell. This material also shows a high ZT of 2.3 ± 0.3 along the c axis but a significantly reduced ZT of 0.8 ± 0.2 along the a axis. We attribute the remarkably high ZT along the b axis to the intrinsically ultralow lattice thermal conductivity in SnSe. The layered structure of SnSe derives from a distorted rock-salt structure, and features anomalously high Grüneisen parameters, which reflect the anharmonic and anisotropic bonding. We attribute the exceptionally low lattice thermal conductivity (0.23 ± 0.03 W m
−1 K−1 at 973 K) in SnSe to the anharmonicity. These findings highlight alternative strategies to nanostructuring for achieving high thermoelectric performance. [ABSTRACT FROM AUTHOR]- Published
- 2014
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10. High-performance bulk thermoelectrics with all-scale hierarchical architectures.
- Author
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Biswas, Kanishka, He, Jiaqing, Blum, Ivan D., Wu, Chun-I, Hogan, Timothy P., Seidman, David N., Dravid, Vinayak P., and Kanatzidis, Mercouri G.
- Subjects
NANOSTRUCTURES ,THERMOELECTRIC materials ,THERMOELECTRICITY ,PHONON scattering ,TRANSMISSION electron microscopy ,THERMAL conductivity - Abstract
With about two-thirds of all used energy being lost as waste heat, there is a compelling need for high-performance thermoelectric materials that can directly and reversibly convert heat to electrical energy. However, the practical realization of thermoelectric materials is limited by their hitherto low figure of merit, ZT, which governs the Carnot efficiency according to the second law of thermodynamics. The recent successful strategy of nanostructuring to reduce thermal conductivity has achieved record-high ZT values in the range 1.5-1.8 at 750-900 kelvin, but still falls short of the generally desired threshold value of 2. Nanostructures in bulk thermoelectrics allow effective phonon scattering of a significant portion of the phonon spectrum, but phonons with long mean free paths remain largely unaffected. Here we show that heat-carrying phonons with long mean free paths can be scattered by controlling and fine-tuning the mesoscale architecture of nanostructured thermoelectric materials. Thus, by considering sources of scattering on all relevant length scales in a hierarchical fashion-from atomic-scale lattice disorder and nanoscale endotaxial precipitates to mesoscale grain boundaries-we achieve the maximum reduction in lattice thermal conductivity and a large enhancement in the thermoelectric performance of PbTe. By taking such a panoscopic approach to the scattering of heat-carrying phonons across integrated length scales, we go beyond nanostructuring and demonstrate a ZT value of ?2.2 at 915 kelvin in p-type PbTe endotaxially nanostructured with SrTe at a concentration of 4 mole per cent and mesostructured with powder processing and spark plasma sintering. This increase in ZT beyond the threshold of 2 highlights the role of, and need for, multiscale hierarchical architecture in controlling phonon scattering in bulk thermoelectrics, and offers a realistic prospect of the recovery of a significant portion of waste heat. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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11. Enhancement of Thermoelectric Figure of Merit by the Insertion of MgTe Nanostructures in p-type PbTe Doped with Na2Te.
- Author
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Ohta, Michihiro, Biswas, Kanishka, Lo, Shih-Han, He, Jiaqing, Chung, Duck Young, Dravid, Vinayak P., and Kanatzidis, Mercouri G.
- Abstract
The thermoelectric properties of crystalline melt-grown ingots of p-type PbTe- xMgTe ( x = 1-3 mol%) doped with Na
2 Te (1-2 mol%) were investigated over the temperature range of 300 K to 810 K. While the powder X-ray diffraction patterns show that all samples crystallize in the NaCl-type structure with no MgTe or other phases present, transmission electron microscopy reveals ubiquitous MgTe nanoprecipitates in the PbTe. The very small amounts of MgTe in PbTe have only a small effect on the electrical transport properties of the system, while they have a large effect on thermal transport significantly reducing the lattice thermal conductivity. A ZT of 1.6 at 780 K is achieved for the PbTe containing 2% MgTe doped with 2% Na2 Te. [ABSTRACT FROM AUTHOR]- Published
- 2012
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12. High Thermoelectric Performance in PbSe–NaSbSe2 Alloys from Valence Band Convergence and Low Thermal Conductivity.
- Author
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Slade, Tyler J., Bailey, Trevor P., Grovogui, Jann A., Hua, Xia, Zhang, Xiaomi, Kuo, Jimmy Jiahong, Hadar, Ido, Snyder, G. Jeffrey, Wolverton, Chris, Dravid, Vinayak P., Uher, Ctirad, and Kanatzidis, Mercouri G.
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VALENCE bands ,THERMOELECTRIC materials ,PHOTOELECTRON spectroscopy ,MELTING points ,THERMAL conductivity ,ALLOYS ,CRYSTAL grain boundaries ,ELECTRICAL conductivity measurement - 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 (NaPbmSbSem+2) are described and the most promising p‐type PbSe‐based thermoelectrics are found among them. Surprisingly, it is observed that below 500 K, NaPbmSbSem+2 exhibits unorthodox semiconducting‐like electrical conductivity, despite possessing degenerate carrier densities of ≈1020 cm−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 NaSbSe2 in PbSe augments both the thermoelectric properties while maintaining a rock salt structure. Namely, density functional theory calculations and photoemission spectroscopy demonstrate that introduction of NaSbSe2 lowers 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‐1 K‐1 between 400 and 873 K without nanostructures. As a consequence, NaPb10SbSe12 achieves maximum ZT ≈1.4 near 900 K when optimally doped. More importantly, NaPb10SbSe12 maintains high ZT across a broad temperature range, giving an estimated record ZTavg of ≈0.64 between 400 and 873 K, a significant improvement over existing p‐type PbSe thermoelectrics. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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13. Thermoelectric Materials: Enhancement of Thermoelectric Figure of Merit by the Insertion of MgTe Nanostructures in p-type PbTe Doped with Na2Te (Adv. Energy Mater. 9/2012).
- Author
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Ohta, Michihiro, Biswas, Kanishka, Lo, Shih-Han, He, Jiaqing, Chung, Duck Young, Dravid, Vinayak P., and Kanatzidis, Mercouri G.
- Published
- 2012
- Full Text
- View/download PDF
14. Computational Prediction of High Thermoelectric Performance in Hole Doped Layered GeSe.
- Author
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Shiqiang Hao, Fengyuan Shi, Dravid, Vinayak P., Kanatzidis, Mercouri G., and Wolverton, Christopher
- Subjects
- *
GERMANIUM selenide , *THERMOELECTRIC materials , *DOPED semiconductors , *ELECTRICAL energy , *REFRIGERATION & refrigerating machinery , *THERMAL conductivity , *CRYSTALLOGRAPHY - Abstract
Thermoelectric materials enable direct conversion between thermal and electrical energy and provide a viable route for power generation and electric refrigeration. In this paper, we use first-principles based methods to predict a very high figure of merit (ZT) performance in hole doped GeSe crystals along the crystallographic b-axis, with maximum ZT ranging from 0.8 at 300 K to 2.5 at 800 K. This extremely high thermoelectric performance is due to a threefold synergy of properties in this material: (1) the exceptionally low lattice thermal conductivity in GeSe due to anharmonicity of vibrational modes, (2) the increased electrical conductivity due to hole doping and increased carrier concentration, and (3) an enhanced Seebeck coefficient via a multiband effect induced by hole doping. The predicted ZT results of hole-doped GeSe are higher than that of hole doped SnSe, which we have recently reported as having experimentally observed record-breaking thermoelectric efficiency. The overall ZT of hole doped GeSe crystals outperforms all current state-of-the-art thermoelectric materials, and this work provides an urgent computational materials prediction that is in need of experimental testing. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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15. Thermal conductivity in Bi0.5Sb1.5Te3+x and the role of dense dislocation arrays at grain boundaries.
- Author
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Rigui Deng, Xianli Su, Zheng Zheng, Wei Liu, Yonggao Yan, Qingjie Zhang, Dravid, Vinayak P., Uher, Ctirad, Kanatzidis, Mercouri G., and Xinfeng Tang
- Subjects
- *
THERMAL conductivity , *THERMAL properties , *THERMOELECTRIC materials , *THERMOELECTRIC power , *CRYSTAL grain boundaries - Abstract
The article cites a research study that examines thermal conductivity in thermoelectric materials and the role of dense dislocation arrays at grain boundaries. It is said that the figure of merit for thermoelectric materials is improved by many prominent mechanisms for reduction in thermal conductivity.
- Published
- 2018
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16. High ZT in p-Type (PbTe)1-2x(PbSe)x(PbS)x Thermoelectric Materials.
- Author
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Korkosz, Rachel J., Chasapis, Thomas C., Shih-han Lo, Doak, Jeff W., Yoon Jun Kim, Chun-I Wu, Euripidis Hatzikraniotis, Hogan, Timothy P., Seidman, David N., Wolverton, Chris, Dravid, Vinayak P., and Kanatzidis, Mercouri G.
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LEAD chalcogenides , *THERMOELECTRIC materials , *THERMAL conductivity , *THERMAL conductivity measurement , *TERNARY system , *POWER factor measurement , *NANOSTRUCTURES - Abstract
Lead chalcogenide thermoelectric systems have been shown to reach record high figure of merit values via modification of the band structure to increase the power factor or via nanostructuring to reduce the thermal conductivity. Recently, (PbTe)1-2x(PbSe)x(PbS)x was reported to reach high power factors via a delayed onset of interband crossing. Conversely, the (PbTe)1-2x(PbSe)x(PbS)x was reported to achieve low thermal conductivities arising from extensive nanostructuring. Here we report the thermoelectric properties of the pseudoternary 2% Na-doped (PbTe)1-2x(PbSe)x(PbS)x system. The (PbTe)1-2x(PbSe)x(PbS)x system is an excellent platform to study phase competition between entropically driven atomic mixing (solid solution behavior) and enthalpy-driven phase separation. We observe that the thermoelectric properties of the PbTe-PbSe-PbS 2% Na doped are superior to those of 2% Na-doped PbTe-PbSe and PbTe-PbS, respectively, achieving a ZT ≈2.0 at 800 K. The material exhibits an increased the power factor by virtue of valence band modification combined with a very reduced lattice thermal conductivity deriving from alloy scattering and point defects. The presence of sulfide ions in the rock-salt structure alters the band structure and creates a plateau in the electrical conductivity and thermopower from 600 to 800 K giving a power factor of 27 μW/cmK2. The very low total thermal conductivity values of 1.1 W/m∙K of the x = 0.07 composition is accounted for essentially by phonon scattering from solid solution defects rather than the assistance of endotaxial nanostructures. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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17. Thermoelectrics with Earth Abundant Elements: High Performance p-type PbS Nanostructured with SrS and CaS.
- Author
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Li-Dong Zhao, Jiaqing He, Wu, Chun-I., Hogan, Timothy P., Xiaoyuan Zhou, Uher, Ctirad, Dravid, Vinayak P., and Kanatzidis, Mercouri G.
- Subjects
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THERMOELECTRICITY , *LEAD sulfide , *THERMAL conductivity , *ELECTRIC properties of nanostructured materials , *THERMAL properties of nanostructured materials , *CHALCOGENIDES , *CALCIUM sulfide , *STRONTIUM - Abstract
We report high thermoelectric performance in nanostructured p-type PbS, a material consisting of highly earth abundant and inexpensive elements. The high level of Na doping switched intrinsic n-type PbS to p-type and substantially raised the power factor maximum for pure PbS to ~9.0 μW cm-1 K-2 at >723 K using 2.5 at. % Na as the hole dopant. Contrary to that of PbTe, no enhancement in the Hall coefficient occurs at high temperature for heavily doped p-type PbS, indicating a single band model and no heavy hole band. We also report that the lattice thermal conductivity of PbS can be greatly reduced by adding SrS or CaS, which form a combination of a nanostructured/solid solution material as determined by transmission electron microscopy. We find that both nanoscale precipitates and point defects play an important role in reducing the lattice thermal conductivity, but the contribution from nanoscale precipitates of SrS is greater than that of CaS, whereas the contribution from point defects in the case of CaS is greater than that of SrS. Theoretical calculations of the lattice thermal conductivity based on the modified Callaway model reveal that both nanostructures and point defects (solid solution) effectively scatter phonons in this system. The lattice thermal conductivity at 723 K can be reduced by ~50% by introducing up to 4.0 at. % of either SrS or CaS. As a consequence, ZT values as high as 1.22 and 1.12 at 923 K can be achieved for nominal Pb0.975Na0.025S with 3.0 at. % SrS and CaS, respectively. No deterioration was observed after a 15 d annealing treatment of the samples, indicating the excellent thermal stability for these high performance thermoelectrics. The promising thermoelectric properties of nanostructured PbS point to a robust low cost alternative to other high performance thermoelectric materials. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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18. High Performance Thermoelectrics from Earth-Abundant Materials: Enhanced Figure of Merit in PbS by Second Phase Nanostructures.
- Author
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Li-Dong Zhao, Shih-Han Lo, Jiaqing He, Hao Li, Biswas, Kanishka, Androulakis, John, Wu, Chun-I., Hogan, Timothy P., Duck-Young Chung, Dravid, Vinayak P., and Kanatzidis, Mercouri G.
- Subjects
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THERMOELECTRIC materials , *LEAD sulfide , *THERMOELECTRICITY , *THERMAL conductivity , *DOPED semiconductors - Abstract
Lead sulfide, a compound consisting of elements with high natural abundance, can be converted into an excellent thermoelectric material. We report extensive doping studies, which show that the power factor maximum for pure n-type PbS can be raised substantially to 12 μW cm-1 K-2 at >723 K using 1.0 mol % PbCl2 as the electron donor dopant. We also report that the lattice thermal conductivity of PbS can be greatly reduced by adding selected metal sulfide phases. The thermal conductivity at 723 K can be reduced by 50%, 52%, 30%, and 42% through introduction of up to 5.0 mol % Bi2S3, Sb2S3, SrS, and CaS, respectively. These phases form as nanoscale precipitates in the PbS matrix, as confirmed by transmission electron microscopy (TEM), and the experimental results show that they cause huge phonon scattering. As a consequence of this nanostructuring, ZT values as high as 0.8 and 0.78 at 723 K can be obtained for nominal bulk PbS material. When processed with spark plasma sintering, PbS samples with 1.0 mol % Bi2S3 dispersion phase and doped with 1.0 mol % PbCl2 show even lower levels of lattice thermal conductivity and further enhanced ZT values of 1.1 at 923 K. The promising thermoelectric properties promote PbS as a robust alternative to PbTe and other thermoelectric materials. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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19. High Performance Na-doped PbTe-PbS Thermoelectric Materials: Electronic Density of States Modification and Shape-Controlled Nanostructures.
- Author
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Girard, Steven N., Jiaqing He, Xiaoyuan Zhou, Shoemaker, Daniel, Jaworski, Christopher M., Uher, Ctirad, Dravid, Vinayak P., Heremans, Joseph P., and Kanatzidis, Mercouri G.
- Subjects
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THERMOELECTRIC materials , *ELECTRIC charge , *NANOSTRUCTURES , *THERMAL conductivity , *SOLUBILITY , *X-ray diffraction - Abstract
Thermoelectric heat-to-power generation is an attractive option for robust and environmentally friendly renewable energy production. Historically, the performance of thermoelectric materials has been limited by low efficiencies, related to the thermoelectric figure-of-merit ZT. Nanostructuring thermoelectric materials have shown to enhance ZT primarily via increasing phonon scattering, beneficially reducing lattice thermal conductivity, Conversely, density-of-states (DOS) engineering has also enhanced electronic transport properties. However, successfully joining the two approaches has proved elusive. Herein) we report a thermoelectric materials system whereby we can control both nanostructure formations to effectively reduce thermal conductivity, while concurrently modifying the electronic structure to significantly enhance thermoelectric power factor. We report that the thermoelectric system PbTe-PbS 12% doped with 2% Na produces shape-controlled cubic PbS nanostructures, which help reduce lattice thermal conductivity, while altering the solubiity of PbS within the PbTe matrix beneficially modifies the DOS that allow for enhancements in thermoelectric power factor. These concomitant and synergistic effects result in a maximum ZT for 2% Na-doped PbTe-PbS 12% of 1.8 at 800 K. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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- View/download PDF
20. On the Origin of Increased Phonon Scattering in Nanostructured PbTe Based Thermoelectric Materials.
- Author
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Jiaqing He, Sootsman, Joseph R., Girard, Steven N., Jin-Cheng Zheng, Jianguo Wen, Yimei Zhu, Kanatzidis, Mercouri G., and Dravid, Vinayak P.
- Subjects
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THERMOELECTRIC materials , *LEAD telluride crystals , *PHONONS , *NANOSTRUCTURES , *NANOPARTICLES , *THERMAL conductivity - Abstract
We have investigated the possible mechanisms of phonon scattering by nanostructures and defects in PbTe-X (X = 2% Sb, Bi, or Pb) thermoelectric materials systems. We find that among these three compositions, PbTe-2% Sb has the lowest lattice thermal conductivity and exhibits a larger strain and notably more misfit dislocations at the precipitate/PbTe interfaces than the other two compositions. In the PbTe-Bi 2% sample, we infer some weaker phonon scattering BiTe precipitates, in addition to the abundant Bi nanostructures. In the PbTe-Pb 2% sample, we also find that pure Pb nanoparticles exhibit stronger phonon scattering than nanostructures with Te vacancies. Within the accepted error range, the theoretical calculations of the lattice thermal conductivity in the three systems are in close agreement with the experimental measurements, highlighting the important role of misfit dislocations, nanoscale particles, and associated interfacial elastic strain play in phonon scattering. We further propose that such particle-induced local elastic perturbations interfere with the phonon propagation pathway, thereby contributing to further reduction in lattice thermal conductivity, and consequently can enhance the overall thermoelectric figure of merit. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
21. Exploring Resonance Levels and Nanostructuring in the PbTe-CdTe System and Enhancement of the Thermoelectric Figure of Merit.
- Author
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Kyunghan Ahn, Mi-Kyung Han, Jiaqing He, Androulakis, John, Ballikaya, Sedat, Uher, Ctirad, Dravid, Vinayak P., and Kanatzidis, Mercouri G.
- Subjects
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NANOSTRUCTURED materials , *THERMOELECTRICITY , *CADMIUM , *ATOMS , *ROCK salt , *TRANSMISSION electron microscopy , *THERMAL conductivity - Abstract
We explored the effect of Cd substitution on the thermoelectric properties of PbTe in an effort to test a theoretical hypothesis that Cd atoms on Pb sites of the rock salt lattice can increase the Seebeck coefficient via the formation of a resonance level in the density of states near the Fermi energy. We find that the solubility of Cd is less than previously reported, and CdTe precipitation occurs to create nanostructuring, which strongly suppresses the lattice thermal conductivity. We present detailed characterization including structural and spectroscopic data, transmission electron microscopy, and thermoelectric transport properties of samples of PbTe-x% CdTe-0.055% Pbl2 (x = 1,3, 5, 7, 10), PbTe-1% CdTe-y% Pbl2 (y = 0.03, 0.045, 0.055, 0.08, 0.1,0.2), PbTe-5% CdTe-y% Pbl2 (y = 0.01,0.03, 0.055, 0.08), and PbTe-1% CdTe-z% Sb (z = 0.3, 0.5, 1, 1.5, 2, 3, 4, 5, 6). All samples follow the Pisarenko relationship, and no enhancement of the Seebeck coefficient was observed that could be attributed to a resonance level or a distortion in the density of states. A maximum ZT of ~1.2 at ~720 K was achieved for the PbTe-1% CdTe-0.055% Pbl2 sample arising from a high power factor of ~17 µW/(cm K²) and a very low lattice thermal conductivity of ~0.5 W/(m K) at ~720 K. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
22. Role of Self-Organization, Nanostructuring, and Lattice Strain on Phonon Transport in NaPb18-xSnxBiTe20 Thermoelectric Materials.
- Author
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Jiaqing He, Aurelie Gueguen, Sootsman, Joseph R., Jin-cheng Zheng, Lijun Wu, Yimei Zhu, Kanatzidis, Mercouri G., and Dravid, Vinayak P.
- Subjects
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PHONONS , *THERMOELECTRIC materials , *TRANSMISSION electron microscopy , *NANOSTRUCTURES , *DENSITY functionals , *THERMAL conductivity - Abstract
Abstract: The composition and microstructure of five thermoelectric materials, PbTe, SnTe, NaPb0.65Sn0.35Te and NaPb18-xSnxBiTe20 (x = 5, 9), were investigated by advanced transmission electron microcopy. We confirm that the pure PbTe, SnTe, and NaPb0.65Sn0.35BiTe have a uniform crystalline structure and homogeneous compositions without any nanoscale inclusions. On the other hand, the nominal NaPb9Sn9BiTe20 phase contains extensive inhomogeneities and nanostructures with size distribution of 3-7 nm. We find that the chemical architecture of the NaPb13Sn5BiTe20 member of the series to be more complex; besides nanoscale precipitates, self-organized lamellar structures are present which were identified as PbTe and SnTe by composition analysis and transmission electron microscopy image simulations. Density functional theory calculations suggest that the arrangement of the lamellar structures conforms to the lowest total energy configuration. Geometric-phase analyses revealed large distributed elastic strain around the nanoscale inclusions and lamellar structures. We propose that interface-induced elastic perturbations in the matrix play a decisive role in affecting the phonon-propagation pathways. The interfaces further enhance phonon scattering which, in turn, reduces the lattice thermal conductivity in these systems that directly results directly in improvement in the thermoelectric figure of merit. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
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