Aaron D. LaLonde
California Institute of Technology
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Featured researches published by Aaron D. LaLonde.
Nature | 2011
Yanzhong Pei; Xiaoya Shi; Aaron D. LaLonde; Heng Wang; Lidong Chen; G. Jeffrey Snyder
Thermoelectric generators, which directly convert heat into electricity, have long been relegated to use in space-based or other niche applications, but are now being actively considered for a variety of practical waste heat recovery systems—such as the conversion of car exhaust heat into electricity. Although these devices can be very reliable and compact, the thermoelectric materials themselves are relatively inefficient: to facilitate widespread application, it will be desirable to identify or develop materials that have an intensive thermoelectric materials figure of merit, zT, above 1.5 (ref. 1). Many different concepts have been used in the search for new materials with high thermoelectric efficiency, such as the use of nanostructuring to reduce phonon thermal conductivity, which has led to the investigation of a variety of complex material systems. In this vein, it is well known that a high valley degeneracy (typically ≤6 for known thermoelectrics) in the electronic bands is conducive to high zT, and this in turn has stimulated attempts to engineer such degeneracy by adopting low-dimensional nanostructures. Here we demonstrate that it is possible to direct the convergence of many valleys in a bulk material by tuning the doping and composition. By this route, we achieve a convergence of at least 12 valleys in doped PbTe1 − xSex alloys, leading to an extraordinary zT value of 1.8 at about 850 kelvin. Band engineering to converge the valence (or conduction) bands to achieve high valley degeneracy should be a general strategy in the search for and improvement of bulk thermoelectric materials, because it simultaneously leads to a high Seebeck coefficient and high electrical conductivity.
Energy and Environmental Science | 2011
Yanzhong Pei; Aaron D. LaLonde; Shiho Iwanaga; G. Jeffrey Snyder
Thermoelectric transport properties of p-type PbTe:Na, with high hole concentrations of approximately 1020 cm−3, are reinvestigated from room temperature to 750 K. The greatly enhanced Seebeck coefficient at these doping levels can be understood by the presence of a sharp increase in the density of states around the Fermi level. As a result, the thermoelectric figure of merit, zT, reaches ∼1.4 at 750 K. The influence of these heavy hole carriers may contribute to a similarly high zT observed in related p-type PbTe-based systems such as Tl-doped PbTe and nanostructured composite materials.
Advanced Materials | 2011
Heng Wang; Yanzhong Pei; Aaron D. LaLonde; G. Jeffrey Snyder
PbSe was expected to have a smaller bandgap and higher thermalconductivity than PbTe. Instead, these values are about the same at high temperature leading to comparable thermoelectric figure of merit, with zT> 1 achieved in heavily doped p-type PbSe.
Materials Today | 2011
Aaron D. LaLonde; Yanzhong Pei; Heng Wang; G. Jeffrey Snyder
The opportunity to use solid-state thermoelectrics for waste heat recovery has reinvigorated the field of thermoelectrics in tackling the challenges of energy sustainability. While thermoelectric generators have decades of proven reliability in space, from the 1960s to the present, terrestrial uses have so far been limited to niche applications on Earth because of a relatively low material efficiency. Lead telluride alloys were some of the first materials investigated and commercialized for generators but their full potential for thermoelectrics has only recently been revealed to be far greater than commonly believed. By reviewing some of the past and present successes of PbTe as a thermoelectric material we identify the issues for achieving maximum performance and successful band structure engineering strategies for further improvements that can be applied to other thermoelectric materials systems.
Advanced Materials | 2011
Yanzhong Pei; Aaron D. LaLonde; Nicholas A. Heinz; Xiaoya Shi; Shiho Iwanaga; Heng Wang; Lidong Chen; G. Jeffrey Snyder
The band structure of PbTe can be manipulated by alloying with MgTe to control the band degeneracy. This is used to stabilize the optimal carrier concentration, making it less temperature dependent, demonstrating a new strategy to improve overall thermoelectric efficiency over a broad temperature range.
Review of Scientific Instruments | 2011
Shiho Iwanaga; Eric S. Toberer; Aaron D. LaLonde; G. Jeffrey Snyder
A high temperature Seebeck coefficient measurement apparatus with various features to minimize typical sources of error is designed and built. Common sources of temperature and voltage measurement error are described and principles to overcome these are proposed. With these guiding principles, a high temperature Seebeck measurement apparatus with a uniaxial 4-point contact geometry is designed to operate from room temperature to over 1200 K. This instrument design is simple to operate, and suitable for bulk samples with a broad range of physical types and shapes.
Proceedings of the National Academy of Sciences of the United States of America | 2012
Heng Wang; Yanzhong Pei; Aaron D. LaLonde; G. Jeffrey Snyder
PbSe is a surprisingly good thermoelectric material due, in part, to its low thermal conductivity that had been overestimated in earlier measurements. The thermoelectric figure of merit, zT, can exceed 1 at high temperatures in both p-type and n-type PbSe, similar to that found in PbTe. While the p-type lead chalcogenides (PbSe and PbTe) benefit from the high valley degeneracy (12 or more at high temperature) of the valence band, the n-type versions are limited to a valley degeneracy of 4 in the conduction band. Yet the n-type lead chalcogenides achieve a zT nearly as high as the p-type lead chalcogenides. This effect can be attributed to the weaker electron–phonon coupling (lower deformation potential coefficient) in the conduction band as compared with that in the valence band, which leads to higher mobility of electrons compared to that of holes. This study of PbSe illustrates the importance of the deformation potential coefficient of the charge-carrying band as one of several key parameters to consider for band structure engineering and the search for high performance thermoelectric materials.
Energy and Environmental Science | 2011
Aaron D. LaLonde; Yanzhong Pei; G. Jeffrey Snyder
Thermoelectric transport properties of n-type PbTe1−xIx with carrier concentrations ranging from 5.8 × 1018–1.4 × 1020 cm−3 are reinvestigated from room temperature to 800 K. The electronic transport properties, resistivity and Seebeck coefficient in this study are effectively consistent with prior reports, however the thermal conductivity has been found to be historically overestimated. The reassessment of the thermal transport properties, in combination with careful control of the carrier density by iodine doping, reveals a significantly larger figure of merit, zT ∼ 1.4, than often previously reported for n-type PbTe. The results and analysis of the data from this study lead to a redetermination of zT for this historical thermoelectric material and provide a renewed interest in n-type PbTe based materials.
Journal of the American Chemical Society | 2012
Maria Ibáñez; Reza Zamani; Aaron D. LaLonde; Doris Cadavid; Wenhua Li; Alexey Shavel; Jordi Arbiol; Joan Ramon Morante; Stéphane Gorsse; G. Jeffrey Snyder; Andreu Cabot
A synthetic route for producing Cu(2)ZnGeSe(4) nanocrystals with narrow size distributions and controlled composition is presented. These nanocrystals were used to produce densely packed nanomaterials by hot-pressing. From the characterization of the thermoelectric properties of these nanomaterials, Cu(2)ZnGeSe(4) is demonstrated to show excellent thermoelectric properties. A very preliminary adjustment of the nanocrystal composition has already resulted in a figure of merit of up to 0.55 at 450 °C.
Energy and Environmental Science | 2011
Yanzhong Pei; Nicholas A. Heinz; Aaron D. LaLonde; G. Jeffrey Snyder
The complexity of the valence band structure in p-type PbTe has been shown to enable a significant enhancement of the average thermoelectric figure of merit (zT) when heavily doped with Na. It has also been shown that when PbTe is nanostructured with large nanometer sized Ag2Te precipitates there is an enhancement of zT due to phonon scattering at the interfaces. The enhancement in zT resulting from these two mechanisms is of similar magnitude but, in principle, decoupled from one another. This work experimentally demonstrates a successful combination of the complexity in the valence band structure with the addition of nanostructuring to create a high performance thermoelectric material. These effects lead to a high zT over a wide temperature range with peak zT > 1.5 at T > 650 K in Na-doped PbTe/Ag2Te. This high average zT produces 30% higher efficiency (300–750 K) than pure Na-doped PbTe because of the nanostructures, while the complex valence band structure leads to twice the efficiency as the related n-type La-doped PbTe/Ag2Te without such band structure complexity.