Thermal and Optical Energy Gaps in PbTe

Tauber, R. N.; Machonis, A.; Cadoff, I.

doi:10.1063/1.1708150

Cited by 132 publications

(81 citation statements)

References 19 publications

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“…Optical absorption edge spectroscopy in semiconductors is a more direct route to obtain information about electronic states near the band edge and specifically information concerning the value of the band gap E g . Optical data on single crystalline bulk samples and films of lead chalcogenides have been obtained using a variety of measurement techniques, [24][25][26][27][28][29][30] but the analysis of these results, including the reported observation of band convergence, have recently been questioned. 8,10 Here, we perform measurements using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) on polycrystalline samples and use ab initio molecular dynamics (AIMD) to study the temperature dependent gap and to examine the band structure at high temperatures.…”

mentioning

confidence: 99%

Temperature dependent band gap in PbX (X = S, Se, Te)

Gibbs¹,

Kim²,

Wang³

et al. 2013

Applied Physics Letters

158

124

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PbTe is an important thermoelectric material for power generation applications due its high conversion efficiency and reliability. Its extraordinary thermoelectric performance is attributed to band convergence of the light L and heavy Σ bands. However, the temperature at which these bands converge is disputed. In this letter, we provide direct experimental evidence combined with ab initio calculations that confirm an increasing optical gap up to 673 K and predict a band convergence temperature of 700 K, much higher than previous measurements showing saturation and band convergence at 450 K.

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mentioning

confidence: 99%

Temperature dependent band gap in PbX (X = S, Se, Te)

Gibbs¹,

Kim²,

Wang³

et al. 2013

Applied Physics Letters

158

124

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“…This difference explains the higher power factor of GeTe by ∼ 30% at T4~650 K (Figure 6b) without involving the complexity of the temperature-dependent energy offset between these two bands in these compounds. 82,86,87 Therefore, the lower effective mass can be considered the main reason for the superior TE performance in cubic GeTe (at high temperatures). For low temperatures, because of the overall high valley degeneracy (N v ) with a sufficiently low effective mass (Table 1) for the dominant Σ valence band in rhombohedral GeTe (Figure 2), the power factor remains slightly higher.…”

Section: Resultsmentioning

confidence: 99%

Electronic origin of the high thermoelectric performance of GeTe among the p-type group IV monotellurides

et al. 2017

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PbTe and SnTe in their p-type forms have long been considered high-performance thermoelectrics, and both of them largely rely on two valence bands (the first band at L point and the second one along the Σ line) participating in the transport properties. This work focuses on the thermoelectric transport properties inherent to p-type GeTe, a member of the group IV monotellurides that is relatively less studied. Approximately 50 GeTe samples have been synthesized with different carrier concentrations spanning from 1 to 20 × 10 20 cm − 3 , enabling an insightful understanding of the electronic transport and a full carrier concentration optimization for the thermoelectric performance. When all of these three monotellurides (PbTe, SnTe and GeTe) are fully optimized in their p-type forms, GeTe shows the highest thermoelectric figure of merit (zT up to 1.8). This is due to its superior electronic performance, originating from the highly degenerated Σ band at the band edge in the low-temperature rhombohedral phase and the smallest effective masses for both the L and Σ bands in the high-temperature cubic phase. The high thermoelectric performance of GeTe that is induced by its unique electronic structure not only provides a reference substance for understanding existing research on GeTe but also opens new possibilities for the further improvement of the thermoelectric performance of this material.

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“…This can be explained by the increasing effective mass of carriers because of the temperature dependent mass of the light bands as well as the transition of holes from the light to the heavy band that has lower mobility. 19,[31][32][33][34][35][36][37][38] Increasing Hall density results in lower electrical resistivity in PbTe:Na/Ag 2 Te nanocomposites, as shown in Fig. 4.…”

Section: Broader Contextmentioning

confidence: 99%

“…The electronic transport, optical spectroscopy and other properties of p-PbTe can be well described by this two-valence-band mode. [31][32][33][34][35][36][37][38] Rather than the Seebeck coefficient being proportional to absolute temperature (e.g. n-type PbTe:La/Ag 2 Te in Fig.…”

Section: Broader Contextmentioning

confidence: 99%

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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Thermal and Optical Energy Gaps in PbTe

Cited by 132 publications

References 19 publications

Temperature dependent band gap in PbX (X = S, Se, Te)

Temperature dependent band gap in PbX (X = S, Se, Te)

Electronic origin of the high thermoelectric performance of GeTe among the p-type group IV monotellurides

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

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