Thermoelectric Properties Of PbTe Research Articles

Mechanical properties of medium-temperature thermoelectric materials based on tin and lead tellurides

The strength and thermoelectric properties of PbTe and Sn0.9Pb0.1Te medium-temperature polycrystalline specimens with p and n conductivity types, respectively, have been studied. The specimens have been produced using extrusion and spark plasma sintering. The strength parameters of the materials were studied using uniaxial compression at 20 to 500 °C. The structure of the materials was studied using X-ray diffraction and electron microscopy. The electrical conductivity and the Seebeck coefficient were measured simultaneously using the four-probe and differential methods. The temperature conductivity and the specific heat capacity were measured using the laser flash and differential scanning calorimetry methods. The PbTe and Sn0.9Pb0.1Te materials produced using extrusion and spark plasma sintering prove to be single-phase and have homogeneous compositions. For comparable synthesis methods, the dislocation density in the Sn0.9Pb0.1Te specimens is by an order of magnitude lower than in the PbTe ones. Study of the mechanical properties of n and p conductivity type specimens over a wide temperature range from 20 to 500 °C has shown that their deformation is plastic and has no traces of brittle fracture. For these plastic materials, the strength criterion has been accepted to be the arbitrary yield stress corresponding to the stress at a 0.2% deformation. The 20 °C yield stress of PbTe and Sn0.9Pb0.1Te is far higher for the specimens produced by extrusion. For all the test temperatures and synthesis methods the Sn0.9Pb0.1Te specimens have a higher strength than the PbTe ones. The PbTe and Sn0.9Pb0.1Te specimens produced by extrusion have better thermoelectric properties than the spark plasma sintered ones. The heat conductivity of the PbTe and Sn0.9Pb0.1Te specimens is almost the same regardless of compaction method.

Thickness-Dependent Terahertz Permittivity of Epitaxially Grown PbTe Thin Films

The exceptional thermoelectric properties of PbTe are believed to be associated with the incipient ferroelectricity of this material, which is caused by strong electron–phonon coupling that connects phononic and electronic dynamics. Here, we have used terahertz time-domain spectroscopy measurements to generate complex permittivity spectra for a set of epitaxially grown PbTe thin films with thicknesses between 100 and 500 at temperatures from 10K to 300K. Using a Drude–Lorentz model, we retrieved the physical parameters of both the phononic and electronic contributions to the THz permittivity. We observed a strong decrease, or softening, of the transverse optical phonon mode frequency with decreasing temperature, determining a thickness-independent negative ferroelectric-transition critical temperature, while we found a thickness-dependent anharmonic phonon decay lifetime. The electronic contribution to the permittivity was larger in thinner films, and both the carrier density and mobility increased with decreasing temperature in all films. Finally, we detected a thickness-dependent longitudinal optical phonon mode frequency, indicating the presence of plasmon–phonon coupling.

TOSSPB: Thermoelectric optimization based on scattering-dependent single-parabolic band model

Thermoelectric materials can contribute to the energy generation by converting thermal into electrical energy. However, current thermoelectrics exhibit low efficiency due to their complex intertwined electrical and thermal properties. Diverse first-principles (based on density functional theory [DFT]) and experimental (based on the single parabolic band [SPB] model) optimization strategies have been explored. However, DFT calculations are limited to simple compounds due to their high computational cost and the SPB model commonly assumes that the electron transport is limited by acoustic phonons. Recent studies, however, revealed that other scattering mechanisms can also be dominant in high-performance thermoelectric materials. Here, a graphical user interface (GUI) is presented, and it allows to optimize the thermoelectric performance based on a scattering-dependent single parabolic band model, TOSSPB. In addition to acoustic deformation potential scattering, polar optical phonon and (screened and non-screened) ionized impurity scattering are included. The GUI indicates that the optimization strategies are strongly dependent on the scattering mechanism which can be obtained using the experimental Hall data and Seebeck coefficient of multiple samples. TOSSPB was tested on the thermoelectric properties of PbTe and SnSe. While the electronic properties of PbTe can be limited by acoustic phonons or polar optical phonons, ionized impurity is most likely the dominant scattering mechanism in hole-doped SnSe as recently predicted. By providing understanding for the scattering mechanism, TOSSPB can tailor the optimization strategies in a wide range of thermoelectric materials accelerating the discovery of high-performance thermoelectrics.

The Influence of Structural and Phase Changes on the Thermoelectric Properties of PbTe Doped with CdSe

In this article, the influence of structural and phase changes on the thermoelectric properties of PbTe doped with CdSe compounds of various molar concentrations were studied. The research showed that with a minimum value of the lattice parameter of the formed new phases in the PbTe matrix (at an impurity concentration of 0.5 mol%), the specific electrical conductivity and thermoEMF coefficient have a minimum value. A further increase in concentration leads to an increase in these parameters.

Enhanced Mechanical Properties of Na0.02Pb0.98Te/MoTe2 Thermoelectric Composites Through in-Situ-Formed MoTe2.

Lead telluride (PbTe) is one of the best thermoelectric materials in the intermediate temperature range, which shows great potential for waste heat recycling. However, its low strength and high brittleness limit its large-scale application because the thermoelectric device usually undergoes mechanical vibration, mechanical and/or thermal cycling, and thermal shock in service. In this study, the enhanced mechanical properties and thermoelectric properties of PbTe are realized simultaneously through introducing dispersive transition-metal dichalcogenide MoTe2 (molybdenum telluride). The in-situ-formed MoTe2 precipitations with a size in the range from 2 to 5 μm and the tight and smooth interface between the PbTe matrix and precipitates contribute to the obvious crack deflection, crack bridging, and pull-out of long grains, dissipating more energy during crack propagation and resulting in a tortuous propagation path. Because of the toughening and the dispersion strengthening effect, the compressive strength, bending strength, and fracture toughness of the sample with a composite amount of 1% are 109 MPa and 50 MPa and 0.65 MPa·m1/2, respectively, which are increased by about 37, 117, and 67% compared to the Na0.02Pb0.98Te matrix. Additionally, the in situ MoTe2 precipitates intensify the interface phonon scattering and thus decrease the lattice thermal conductivity. As a result, the Na0.02Pb0.98Te-1%MoTe2 sample achieves a maximum ZT value of 1.46 at 700 K, which is 11% higher than that of Na0.02Pb0.98Te without any MoTe2 nanoprecipitation.

Influence of selenium doping on structural, morphological and thermoelectric properties of nanocrystalline PbTe100−xSex thin films

Nanocrystalline PbTe100−xSex thin films are prepared using an integrated physical–chemical approach by evaporating chemically synthesized PbTe nanopowders on glass substrates. All the deposited films exhibiting the face centered cubic structure with the crystallite orientation along (200) direction. The crystallite size of the films is within the range 10–26 nm. XRD analysis indicated that the lattice constants of PbTe100−xSex thin films decreased with the increasing amount of Se. Raman spectra of these PbTe100−xSex thin films show a wavelength shift in the peak position as compared with PbTe due to the addition of Se in PbTe. Electrical resistivity study reveals that the samples are exhibiting semiconducting nature. The value of the Seebeck coefficient of PbTe100−xSex thin films with x = 0, 6, 10 and 15 is 788, 1101, 921 and 780 µV/K respectively which is high compared to the bulk (265 µV/K). Observed results imply that the thermoelectric properties of PbTe gets enhanced due to doping of Se.

Thermoelectric Properties of PbTe Prepared by Spark Plasma Sintering of Nano Powders

Thermoelectric Properties of PbTe Prepared by Spark Plasma Sintering of Nano Powders

Tailoring the mechanical properties of thermoelectric lead telluride by alloying with non-doping calcium

Thermoelectric generators have a great potential in waste heat recovery and energy harvesting due to their principle of directly converting thermal into electrical energy. Despite a long history in space travel and a broad range of potential applications, TEGs are rarely found in terrestrial applications. Reasons are manufacturing problems and limited durability in dynamic operation conditions due to deficient mechanical properties of the thermoelectric materials, which often suffer from low strength and high brittleness. We present a concept for the basically independent tailoring of mechanical and thermoelectric properties. This can be achieved by the alloying of TE materials with additional elements having preferably no or only little influence on the TE properties. We demonstrate a route of improving the mechanical properties of PbTe by alloying with calcium. It is shown that calcium has minor effects on the thermoelectric properties of PbTe while significantly increasing hardness and fracture strength. As proof of concept, mechanically more stable sodium and calcium co-doped Pb0.966Ca0.02Na0.014Te with ZT exceeding 1.2 above 650 K is demonstrated.

Effects of Sb on the Thermoelectric Properties of PbTe

Effects of Sb on the Thermoelectric Properties of PbTe

Thermoelectric properties of PbTe with indium and bismuth secondary phase

Lead telluride (PbTe) with indium (In) and bismuth (Bi) as micrometer sized secondary phases dispersed throughout the bulk has been prepared by matrix encapsulation method. In and Bi are not found to substitute in PbTe as shown by Rietveld and room temperature Raman studies but are present as secondary phases. Increased values of temperature dependent electrical resistivity and Seebeck coefficient show the effect of interfaces on electronic transport. As expected, thermal conductivity is found to reduce on addition of secondary phases due to a reduced electronic contribution, further confirming that electron scattering at interfaces is more important than phonon scattering in such systems for thermoelectric properties. However, due to the reduction in the power factor of the In and Bi added samples from that of the parent PbTe, the overall thermoelectric figure of merit (zT) does not increase beyond that of PbTe, for which the highest value of 0.7 is obtained at 778 K.

Enhanced Thermoelectric Performance in PbTe–PbS Nanocomposites

Abstract In this study, we investigate the changes occurring in the microstructure and thermoelectric properties of PbTe0.9S0.1 alloy (PbTe–PbS) under varying thermal treatment conditions. Transmission electron microscopy (TEM) studies were utilized to reveal the distribution of nano-precipitates in the annealed alloy. PbTe0.9S0.1 alloy with PbS phase precipitates displayed a significant reduction in the thermal conductivity and an enhancement in the Seebeck coefficient. The 47% reduction in lattice thermal conductivity at the measurement temperature of 300°C in the alloy annealed at 400°C was attributed to the phonon scattering occurring due to the presence of nano-precipitates. The annealed alloy displayed higher electrical conductivity at room temperature than that of the alloy without annealing. The maximum figure of merit, ZT, was found to be 0.76 at 300°C in the alloy annealed at 400°C.

Effect of Sintering Temperature on Thermoelectric Properties of PbTe/Ag Composites Fabricated by Chemical Plating and Spark Plasma Sintering

PbTe/Ag composite powders were synthesized by a chemical plating method and then compacted by spark plasma sintering (SPS) at 573 K to 673 K and 50 MPa. The effects of the sintering temperature on the thermoelectric properties of PbTe and the PbTe/Ag composites were investigated. The thermoelectric properties of PbTe and PbTe/Ag bulk samples were measured in the temperature range from 300 K to 700 K. PbTe/Ag bulk samples changed electrical transport behavior from p-type to n-type at room temperature. The SPS temperature not only changed the lattice parameter but also affected the conduction behavior of PbTe/Ag composites. The variation in the carrier concentration was determined by the role of the Ag dopant for different SPS temperatures. Moreover, the conduction of the PbTe/Ag samples changed from metallic to semiconducting in the measured temperature range from 300 K to 700 K as the sintering temperature increased. For the PbTe/Ag bulk materials subjected to SPS at 573 K and 673 K, the values of the power factor were 0.38 mW/m K2 and 1.31 mW/m K2 at 700 K, respectively.

Anharmonic effects in the thermoelectric properties of PbTe

In this work, we investigate the crystal anharmonic effects in the thermoelectric properties of n-type PbTe. The lattice thermal transport coefficient is computed by employing an isotropic continuum model for the dispersion relation for acoustic as well as optical phonon branches, an isotropic continuum model for crystal anharmonicity, and the single-mode relaxation time scheme. The electronic components of the transport coefficients in a wide temperature range are calculated using the isotropic-nearly-free-electron model, interaction of electrons with deformation potential of acoustic phonons, and the effect of the band non-parabolicity. It is found that the transverse optical branches play a major role in determining the phonon conductivity and the thermoelectric figure of merit of this material.

Fermi surface and electron dispersion of PbTe doped with resonant Tl impurity from KKR-CPA calculations

We present results of detailed study on the electron dispersions and Fermi surface of lead telluride doped with $2\%$ of thallium, which is resonant impurity in PbTe. Using the KKR--CPA method, Bloch spectral functions (BSFs), which replace the dispersion relations in alloys, are calculated, and BSFs intensity maps over the Brillouin zone (alloy Fermi surface cross-sections) are presented. It is shown, that close to the valence band edge, Tl does not create an isolated impurity band, but due to its resonant character, strongly disturbs the host electronic bands, leading to disappearance of sharp and well defined electronic energy bands. Consequences of this effect on the transport properties are discussed and new qualitative explanation of the improvement in thermoelectric properties of PbTe:Tl is suggested.

Effect of aluminum on the thermoelectric properties of nanostructured PbTe

In the present work, the effect of aluminum (Al) on the thermoelectric properties of PbTe is studied. Aluminum doped PbTe samples, fabricated by a ball milling and hot pressing, have Seebeck coefficients between −100 and −200 μV K−1 and electrical conductivities of (3.6–18) × 104 S m−1 at room temperature, which means that Al is an effective donor in PbTe. The first principle calculations clearly show an increase of the density of states close to the Fermi level in the conduction band due to Al doping, which averages up the energy and effective mass of electrons, resulting in enhancement of the Seebeck coefficient. The maximum figure-of-merit ZT of 1.2 is reached at 770 K in the Al0.03PbTe sample.

Thermoelectric properties of PbTe with encapsulated bismuth secondary phase

Lead Telluride (PbTe) with bismuth secondary phase embedded in the bulk has been prepared by matrix encapsulation technique. X-Ray Diffraction results indicated crystalline PbTe, while Rietveld analysis showed that Bi did not substitute at either Pb or Te site, which was further confirmed by Raman and X-Ray Photoelectron Spectroscopy. Scanning Electron Microscopy showed the expected presence of a secondary phase, while Energy Dispersive Spectroscopy results showed a slight deficiency of tellurium in the PbTe matrix, which might have occurred during synthesis due to higher vapor pressure of Te. Transmission Electron Microscopy results did not show any nanometer sized Bi phase. Seebeck coefficient (S) and electrical conductivity (σ) were measured from room temperature to 725 K. A decrease in S and σ with increasing Bi content showed an increased scattering of electrons from PbTe-Bi interfaces, along with a possible electron acceptor role of Bi secondary phase. An overall decrease in the power factor was thus observed. Thermal conductivity, measured from 400 K to 725 K, was smaller at starting temperature with increasing Bi concentration, and almost comparable to that of PbTe at higher temperatures, indicating a more important role of electrons as compared to phonons at PbTe-Bi interfaces. Still, a reasonable zT of 0.8 at 725 K was achieved for undoped PbTe, but no improvement was found for bismuth added samples with micrometer inclusions.

The Thermoelectric Properties of PbTe Doped with Na and PbI2 Elements

In this study, the PbTe samples doped with PbI2 or Na were prepared using powder metallurgical techniques. The preparation procedures were optimized by the experimental results with respect to powder particle size, compaction pressure, and influence of sintering parameters. The power factor profiles of the PbTe samples with different dopant concentration at about 100°C to 250°C were calculated from the measured values of the Seebeck coefficient and the electrical of the samples. The research interpretation to the thermoelectric properties had been transformed by means of the different dopant concentration indeed. The power factor of the N-type samples was better than the P-type samples. For optimization of the power factors presented in the measurements temperature range, the optimized dopant concentration of PbI2 is 0.05 at% and of Na is 0.50 at% respectively.

The effect of chromium impurity on the thermoelectric properties of PbTe in the temperature range 100–600 K

In this work we have investigated the effect of the chromium (Cr) impurity on the thermoelectric properties of lead telluride (PbTe) bulk crystal with different Cr-content. The structural characterization of the crystals was done by x-ray diffraction and high-resolution transmission electron microscopic analyses. The incorporation of Cr in PbTe over the soluble limit has been found to replace Pb from the lattice site, forcing it to be precipitated into nanodots, with their dimensions in the range of 2–13 nm and their numbers increasing with the increase in Cr doping. The transport properties of the samples with different Cr-content have been evaluated through temperature dependent electrical resistivity, the Hall coefficient, and thermopower measurements in the temperature range of 100–600 K. The highest mobility is obtained as 1404 cm2/V s for a sample with a carrier concentration of 3.84 × 1018 cm−3 at 300 K. The high electron mobility and moderately higher value of the thermopower are expected to produce a high power factor of the samples with the highest value of 38.49 × 10−4 Wm−1K−2 in a specimen with a Cr-content of 1.45 at. % at room temperature. The power factor of the specimen with 1.3 at. % Cr-content is found to be above 29 × 10−4 Wm−1K−2 in the wide temperature range of 300–600 K.

Thermoelectric Properties of PbTe, SnTe, and GeTe at High Pressure: an Ab Initio Study

Xiamen University of China; Specialized Research Fund for the Doctoral Program of Higher Education [20090121120028, 20100121120 026]; National Natural Science Foundation of China [11044001]; Natural Science Foundation of Fujian Province, China [2009J01015

Electronic structure of the thermoelectric materials PbTe and AgPb18SbTe20 from first-principles calculations

To investigate the effects of substituting Ag and Sb for Pb on the thermoelectric properties of PbTe, the electronic structures of PbTe and AgPb18SbTe20 were calculated by using the linearized augmented plane wave based on the density-functional theory of the first principles. By comparing the differences in the band structure, the partial density of states (PDOS), the scanning transmission microscope, and the electron density difference for PbTe and AgPb18SbTe20, we explained the reason from the aspect of electronic structures why the thermoelectric properties of AgPb18SbTe20 could be improved significantly. Our results suggest that the excellent thermoelectric properties of AgPb18SbTe20 should be attributed in part to the narrowing of its band gap, band structure anisotropy, the much extrema and large DOS near Fermi energy, as well as the large effective mass of electrons. Moreover, the complex bonding behaviors for which the strong bonds and the weak bonds are coexisted, and the electrovalence and covalence of Pb–Te bond are mixed should also play an important role in the enhancement of the thermoelectric properties of the AgPb18SbTe20.