Morphological evolution of Ag2Te precipitates in thermoelectric PbTe

Lensch-Falk, Jessica L.; Sugar, Joshua D.; Hekmaty, Michelle A.; Medlin, Douglas L.

doi:10.1016/j.jallcom.2010.05.054

Cited by 43 publications

(39 citation statements)

References 53 publications

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“…The plate-like Ag 2 Te precipitates have preferred orientation parallel with <001> directions in the PbTe matrix, consistent with previous reports. 16,19,29 The Ag 2 Te precipitates are nanometer sized in one direction but micron-size in the other directions, which is larger than those generally observed in PbTe/AgSbTe 2 and its analogs. 9,30 No Ag 2 Te precipitates smaller than $50 nm could be found in PbTe/Ag 2 Te system with similar synthesis conditions.…”

Section: Broader Contextmentioning

confidence: 74%

Combination of large nanostructures and complex band structure for high performance thermoelectric lead telluride

Pei

Heinz

LaLonde

et al. 2011

Energy Environ. Sci.

165

112

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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 Ag 2 Te 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/Ag 2 Te. 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/Ag 2 Te without such band structure complexity. Thermoelectric (TE) applications have attracted increasing interest in the last decade as a means to combat the ever growing rate of energy consumption throughout the world. The two main applications for thermoelectric materials are power generation, which utilizes the Seebeck effect, and solid state cooling, which has its roots in the Peltier effect. In recent years, thermoelectric power generation has been a prime interest to the automotive industry 1 as a sustainable and emission free route to vehicular waste heat recovery. The effectiveness of this process is restricted by the overall efficiency of the thermoelectric materials.On a materials level, the efficiency of the thermal to electrical energy conversion is determined by the thermoelectric figure of, where S, s, k E and k L are the Seebeck coefficient, electrical conductivity, and the electronic and lattice components of the thermal conductivity. Since S, s and k E have an intimate relationship with the carrier density, 1,2 the grand challenge in designing thermoelectric materials is the decoupling of electronic and thermal properties. Many methods to achieve a large power factor (S 2 s) or to reduce the thermal conductivity were proven to be successful, but combination of these two effects is difficult. As a result, the current best commercially available thermoelectric materials have a peak zT near unity.A number of mechanisms have been proposed to explain high zT in p-type PbTe. The Tl-doping in PbTe:Tl produces resonant electronic states that enhances the Seebeck coefficient, but reduces hole mobility 3 and has zT $ 1.4 at 500 C. Na-doped PbTe:Na, 4 without resonant states, 5,6 has similarly high zT that Materials Science, California Institute of Technology, Pasadena, CA, 91125, USA. E-mail: jsnyder@caltech.edu Broader contextThermoelectric generators, which directly convert heat into electricity are being considered for industrial or automotive waste heat recovery. However, th...

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Section: Broader Contextmentioning

confidence: 74%

Combination of large nanostructures and complex band structure for high performance thermoelectric lead telluride

Pei

Heinz

LaLonde

et al. 2011

Energy Environ. Sci.

165

112

View full text Add to dashboard Cite

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“…1 J-L. Although these nanostructures are coherent, the shapes are quite different; whereas a spherical shape with a diameter of a few nanometers is observed for QH; irregular shapes are shown in the QAH and AH (26) in their study on Ag 2 Te precipitates in a PbTe matrix; they found that Ag 2 Te precipitates form as coherent spherical nanoparticles in the quenched sample, yet these evolve into flattened semicoherent disks in the annealed samples. The sizes of these nanostructures are quantified and shown in Fig.…”

Section: Resultsmentioning

confidence: 97%

Right sizes of nano- and microstructures for high-performance and rigid bulk thermoelectrics

Wang

Bahk

Kang

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

123

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In this paper, we systematically investigate three different routes of synthesizing 2% Na-doped PbTe after melting the elements: (i) quenching followed by hot-pressing (QH), (ii) annealing followed by hot-pressing, and (iii) quenching and annealing followed by hot-pressing. We found that the thermoelectric figure of merit, zT, strongly depends on the synthesis condition and that its value can be enhanced to ∼2.0 at 773 K by optimizing the size distribution of the nanostructures in the material. Based on our theoretical analysis on both electron and thermal transport, this zT enhancement is attributed to the reduction of both the lattice and electronic thermal conductivities; the smallest sizes (2∼6 nm) of nanostructures in the QH sample are responsible for effectively scattering the wide range of phonon wavelengths to minimize the lattice thermal conductivity to ∼0.5 W/m K. The reduced electronic thermal conductivity associated with the suppressed electrical conductivity by nanostructures also helped reduce the total thermal conductivity. In addition to the high zT of the QH sample, the mechanical hardness is higher than the other samples by a factor of around 2 due to the smaller grain sizes. Overall, this paper suggests a guideline on how to achieve high zT and mechanical strength of a thermoelectric material by controlling nano-and microstructures of the material.waste heat recovery | energy harvesting A thermoelectric (TE) device is a solid-state device that converts heat directly into electricity and vice versa (1-5). As there are no moving parts involved and the device configuration is simple, TE devices have demonstrated long-term reliability in various space missions, usually running for tens of years without maintenance (6). However, they are not yet widely used in many other energy conversion applications on earth mainly due to their low conversion efficiencies. The conversion efficiency of a TE device largely depends on the material properties, i.e., the figure of merit (1, 3), zT = [S 2 /ρ(κ L + κ e )]T, where T is the absolute temperature, S is the Seebeck coefficient, ρ is the electrical resistivity, and κ L and κ e are, respectively, the lattice (or phonon) and electronic thermal conductivities. Increasing the zT has proven challenging because the constituent TE properties are interdependent; for example, decreasing the electrical resistivity results in decreasing the Seebeck coefficient and increasing the electronic thermal conductivity.

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“…This is sufficient to enable nucleation of the Ag 2 Te precipitates at intermediate temperatures. Ag is known to be a fast diffusing element in PbSe with D 0 = 7.4·10 −8 m 2 ·s −1 and Q = 33.77 kJ·mole −1 ; valid for the temperature range of 400 through 850 • C [25], where D 0 and Q are the pre-exponential diffusion coefficient and activation energy, respectively. This corresponds to a diffusion length, √ Dt, of ca.…”

Section: Materials Processing and Microstructure Evolutionmentioning

confidence: 99%

“…Thorough investigations of the microstructure formed in PbTe-based ternary and quaternary systems, including its temporal evolution and effects on TE behavior, have been reported [14][15][16][17][18][19][20][21]. Such effects were particularly studied for Ag-alloyed PbTe compounds as well [22][23][24][25][26]. Nevertheless, neither of these studies introduces systematic investigations of the effects of second-phase precipitates' volume fraction, number density, and average size, as well as their temporal evolution, on TE transport properties of PbTe-based alloys.…”

Section: Introductionmentioning

confidence: 99%

Microstructure Evolution of Ag-Alloyed PbTe-Based Compounds and Implications for Thermoelectric Performance

et al. 2017

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Abstract:We investigate the microstructure evolution of Ag-alloyed PbTe compounds for thermoelectric (TE) applications with or without additions of 0.04 at. % Bi. We control the nucleation and temporal evolution of Ag 2 Te-precipitates in the PbTe-matrix applying designated aging heat treatments, aiming to achieve homogeneous dispersion of precipitates with high number density values, hypothesizing that they act as phonon scattering centers, thereby reducing lattice thermal conductivity. We measure the temperature dependence of the Seebeck coefficient and electrical and thermal conductivities, and correlate them with the microstructure. It is found that lattice thermal conductivity of PbTe-based compounds is reduced by controlled nucleation of Ag 2 Te-precipitates, exhibiting a number density value as high as 2.7 × 10 20 m −3 upon 6 h aging at 380 • C. This yields a TE figure of merit value of ca. 1.4 at 450 • C, which is one on the largest values reported for n-type PbTe compounds. Subsequent aging leads to precipitate coarsening and deterioration of TE performance. Interestingly, we find that Bi-alloying improves the alloys' thermal stability by suppressing microstructure evolution, besides the role of Bi-atoms as electron donors, thereby maintaining high TE performance that is stable at elevated service temperatures. The latter has prime technological significance for TE energy conversion.

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Morphological evolution of Ag2Te precipitates in thermoelectric PbTe

Cited by 43 publications

References 53 publications

Combination of large nanostructures and complex band structure for high performance thermoelectric lead telluride

Combination of large nanostructures and complex band structure for high performance thermoelectric lead telluride

Right sizes of nano- and microstructures for high-performance and rigid bulk thermoelectrics

Microstructure Evolution of Ag-Alloyed PbTe-Based Compounds and Implications for Thermoelectric Performance

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