Showing papers on "Lead telluride published in 2021"

High Thermoelectric Performance of p-Type PbTe Enabled by the Synergy of Resonance Scattering and Lattice Softening.

Abstract: In this work, we show the simultaneous enhancement of electrical transport and reduction of phonon propagation in p-type PbTe codoped with Tl and Na. The effective use of advanced electronic structure engineering improves the thermoelectric power factor S2σ over the temperature range from 300 to 825 K. A rise in the Seebeck coefficient S was obtained due to the enhanced effective mass m*, coming from the Tl resonance state in PbTe. Due to the presence of additional carriers brought by Na codoping, electrical conductivity became significantly improved. Furthermore, Tl and Na impurities induced crystal lattice softening, remarkably reducing lattice thermal conductivity, which was confirmed by a measured low speed of sound vm and high internal strain CeXRD. Eventually, the combination of both the attuned electronic structure and the lattice softening effects led to a very high ZT value of up to ∼2.1 for the Pb1-x-yTlxNayTe samples. The estimated energy conversion efficiency shows the extraordinary value of 15.4% (Tc = 300 K, Th = 825 K), due to the significantly improved average thermoelectric figure of merit ZTave = 1.05. This work demonstrates that the combination of impurity resonance scattering and crystal lattice softening can be a breakthrough concept for advancing thermoelectrics.

Origins of low lattice thermal conductivity of Pb1-xSnxTe alloys for thermoelectric applications.

Abstract: Lead telluride is a well-established material for direct conversion of heat into electricity. However, the aspects of the heat transport phenomena for PbTe-alloys remain not fully understood. Here, for the first time, origins of the phonon scattering in Pb1−xSnxTe compounds were studied through changes in the effective anharmonic pair potential obtained from X-ray Absorption Fine Structure (XAFS) spectroscopy. Results indicate that the interatomic pair potential of Pb–Te and Sn–Te bonds changes with the level of substitution x and that the anharmonicity of bonds in the solid solution is increased leading to the lower values of the lattice thermal conductivity. Furthermore, due to the existence of a soft TO mode in Pb1−xSnxTe, the Gruneisen parameter γE determined using XAFS much more precisely corresponds with the changes of lattice thermal conductivity κlat compared to γS obtained from the speed of sound measurements. This study explains the observed drastic reduction in κL in Pb1−xSnxTe solid solution (2.3 W m−1 K−1 for PbTe vs. 1.0 W m−1 K−1 for Pb0.75Sn0.25Te), due to changes in the interatomic pair potential of Pb–Te and Sn–Te and provides guidelines into its effective modification related to thermal transport in alloys based on PbTe. The estimated range of low thermal conductivity for the PbTe–SnTe solid solutions (<1 W m−1 K−1) reveals opportunities for further enhancement of energy conversion for this promising family of compounds. Moreover, this work provides a new concept for the estimation of the Gruneisen parameter through the EXAFS spectra analysis.

Strained Endotaxial PbS Nanoprecipitates Boosting Ultrahigh Thermoelectric Quality Factor in n-Type PbTe As-Cast Ingots.

Abstract: Lead telluride (PbTe) has long been regarded as an excellent thermoelectric material at intermediate temperature range (573-873 K); however, n-type PbTe's performance is always relatively inferior to its p-type counterpart mainly due to their different electronic band structures. In this work, an ultrahigh thermoelectric quality factor (µ/κL ≈ 1.36 × 105 cm3 KJ-1 V-1 ) is reported in extra 0.3% Cu doped n-type (PbTe)0.9 (PbS)0.1 as-cast ingots. Transmission electron microscopy (TEM) characterization reveals that excess PbS exists in PbTe matrix as strained endotaxial nanoprecipitates, which affect electrical and thermal conduction discriminately: (1) coherent PbTe/PbS lattice minimizes the interface scattering of charge carriers; (2) periodic strain centers at PbTe/PbS interface exhibit intensive strain contrast, which can strongly scatter heat-carrying phonons. Electron backscattered diffraction (EBSD) characterization illustrates very large PbTe grains (≈1 mm) in these as-cast ingots, ensuring an extremely low grain boundary scattering rate thus a very high charge carrier mobility. Eventually, a remarkably high ZTmax ≈ 1.5 at 773 K and an outstanding ZTavg ≈ 1.0 between 323 and 773 K are simultaneously achieved in the (PbTe)0.9 (PbS)0.1 +0.3%Cu sample; these values are highly competitive with reported state-of-art n-type PbTe materials.

Effect of surfactant concentration on the morphology and thermoelectric power factor of PbTe nanostructures prepared by a hydrothermal route

Abstract: Hydrothermal method as a facile bottom-up synthesis technique has many advantages for manufacturing various nanomaterials with controlled properties. In this work, lead telluride nanostructures were synthesized via a simple hydrothermal method at different surfactant concentrations. It was observed that the surfactant concentration has considerable effect on the morphology, and size of the synthesized nanostructures and thus the thermoelectric performance. In the present work, several techniques were used to characterize the structure, morphology, composition and optical properties of the synthesized PbTe nanostructures including XRD, TEM, EDS as well as PL and Raman spectroscopy. The electrical and thermoelectric properties were studied in the temperature range from 300 to 550 K. The results demonstrate that increasing the surfactant concentration improves the power factor due to a significant enhancement in the Seebeck coefficient.

Dynamically Tunable Terahertz Emission Enabled by Anomalous Optical Phonon Responses in Lead Telluride

Abstract: Lead telluride (PbTe), a narrow bandgap semiconductor commonly used in infrared detectors, exhibits anomalous vibrational and structural properties, making it appealing for thermoelectrics. Despite...

Te-Embedded Nanocrystalline PbTe Thick Films: Structure and Thermoelectric Properties Relationship

Abstract: The Te-embedded PbTe nanocrystallline thick films (i.e., 50 µm) were electrodeposited, where the fraction and average grain size of PbTe and Te phases were tuned by adjusting the applied potential followed by post thermal treatment. The crystal grain boundary and Te nano-inclusion in the films played critical roles in their thermoelectric properties. The Te-embedded PbTe thick film with the average grain size of around 100 nm showed lower energy barrier height (EB = 0.023 eV) than thick films with the average grain size of a few tens of nm (EB = 0.11). Although decrease in the energy barrier reduced the Seebeck coefficient, however, it enhanced the electrical conductivity, which resulted in an increase in power factor (PF). The highest power factor was 183 μw K−2 cm−1, achieved at the energy barrier of 0.023 eV.

A new binary phase in the tin monoselenide system: chemical epitaxy of orthorhombic γ-SnSe thin films

Abstract: A new orthorhombic binary phase in the tin mono-selenide system, γ-SnSe, was deposited from solution onto an intermediate layer of PbS on GaAs substrates. Its structure is based on orthorhombic lead telluride (PbTe) which was reported to exist at high pressures, yet has never been observed in SnSe. The proposed model of γ-SnSe was experimentally determined using X-ray diffraction with lattice parameters a0 = 0.8332 nm, b0 = 0.4136 nm, c0 = 0.6115 nm, Rp = 5.96, and Rwp = 8.16. The films show heteroepitaxial relations with the underlying layer of PbS.

A comprehensive study of lead telluride (PbTe)-based amorphous alloys: Glass formation and thermoelectric properties

Abstract: Vitrification enables to create complex structure with a large degree of disorder, which provides a new solution to improve the performance of lead telluride (PbTe)-based thermoelectric materials by reducing the lattice thermal conductivity. Yet, it is an extreme challenge to vitrify PbTe-based alloys due to the incomplete knowledge of the glass formation mechanism. Here, the glass formation of PbTe-based alloys is studied by jointly concerning thermodynamics and kinetics. The comparison of (PbTe)x(Ga2Te3)100-x and (PbTe)x(In2Te3)100-x alloys showed that low entropy of fusion(∆Sm) and deep eutectic fashion are the two keys in glass forming ability(GFA). Novel (PbTe)x(Ga2Te3)100-x glasses are prepared and the glass-forming region is identified to be the composition range of x = 52 ~ 64. An extremely low thermal conductivity of the best glass component (PbTe)61(Ga2Te3)39 is determined with the value of ~ 0.1 Wm−1K−1 at 300 K.

Structural complexity and the metal-to-semiconductor transition in lead telluride

Abstract: Lead chalcogenides are known for their thermoelectric properties since the first work of Thomas Seebeck on the discovery of this phenomenon. Yet, the electronic properties of lead telluride are still of interest due to the incomplete understanding of the metal-to-semiconductor transition at temperatures around 230 °C. Here, a temperature-dependent atomic-resolution transmission electron microscopy study performed on a single crystal of lead telluride reveals structural reasons for this electronic transition. Below the transition temperature, the formation of a dislocation network due to shifts of the NaCl-like atomic slabs perpendicular to {100} was observed. The local structure modification leads to the appearance of in-gap electronic states and causes metal-like electronic transport behavior. The dislocation network disappears with increasing temperature, yielding semiconductor-like electrical conductivity, and re-appears after cooling to room temperature restoring the metal-like behavior. The structural defects coupled to the ordering of stereochemically active lone pairs of lead atoms are discussed in the context of dislocations' formation. Lead telluride is an important thermoelectric material but its metal-to-semiconductor transition above 230 °C is not fully understood. Here, atomic-resolution transmission electron microscopy provides structural insights into this transition, explaining the metallic behavior by a dislocation network within the rock salt structure.

Cation interstitial diffusion in lead telluride and cadmium telluride studied by means of neural network potential based molecular dynamics simulations.

Abstract: Using a recently developed approach to represent ab initio based force fields by a neural network potential, we perform molecular dynamics simulations of lead telluride and cadmium telluride crystals. In particular, we study the diffusion of a single cation interstitial in these two systems. Our simulations indicate that the interstitials migrate via two distinct mechanisms: through hops between interstitial sites and through exchanges with lattice atoms. We extract activation energies for both of these mechanisms and show how the temperature dependence of the total diffusion coefficient deviates from Arrhenius behaviour. The accuracy of the neural network approach is estimated by comparing the results for three different independently trained potentials.

Enhanced thermoelectric properties of PbTe0.95via N-type PbS nano-inclusions using a conventional sintering method

Abstract: An N-type lead telluride (PbTe0.95) thermoelectric material prepared by a conventional sintering method (CSM) has been investigated for the first time. N-type nanosized lead sulfide (PbS) fabricated using the one-pot synthesis method was embedded in the PbTe0.95 matrix to enhance the thermoelectric efficiency, zT. It was successfully demonstrated that the CSM could be used to prepare the nanosized n-type PbTe composite with the zT value of ∼1 at 673 K. This value is comparable to the one synthesized using spark plasma sintering and hot press sintering methods. We attribute the enhanced zT to the strong phonon scattering induced by the nanosized PbS. Meanwhile, the nanosized PbS particles, acting as a sintering additive, enhanced the sintering behavior of as-prepared PbTe0.95 powder. It was found that the introduction of 3 wt% nanosized n-type PbS could reduce the lattice thermal conductivity of the pristine sample of PbTe0.95 from 0.914 W m−1 K−1 to 0.59 W m−1 K−1. Finally, a single parabolic band model (SPB) demonstrated that the 3 wt% was the optimized doping amount for the PbS-doped PbTe0.95 composites.

Solution Processed Lead Telluride Nanowires as a Passivating Layer to CdTe Photovoltaics

Abstract: Here, we report the application of lead telluride (PbTe) nanowires (NWs) as a passivating layer to cadmium telluride (CdTe) solar cells enhancing the opto-electronic properties and device performance. The PbTe NWs were synthesized using hot injection colloidal method and applied to CdTe films using a spin-coating process. Steady state photoluminescence (PL) and time resolved photoluminescence (TRPL) measurements from the back side of the device show evidence of passivation in the form of reduced back surface recombination. Devices fabricated using these NWs demonstrate improved open-circuit voltage (V OC ) and fill factor (FF) in agreement with the desired effects of surface passivation.

Two-Color Infrared Sensor on the PbTe: In p-n Junction.

Abstract: A lead telluride sensor was fabricated on the base of a p-n PbTe junction created on a PbTe single crystal grown by the Czochralski technique, followed by the diffusion of an indium donor impurity into a crystal The capacitance-voltage and current-voltage characteristics of the sensor were measured over the temperature range from 80 K to 150 K A prototype of a high-temperature mid-IR sensor, a PbTe diode, with a cut-off wavelength of 4 μm, operating at temperatures up to 150 K, was demonstrated for the first time The advantage of the sensor is that its operating temperature is high enough to be reached by a solid-state thermoelectric cooler The sensor showed a specific detectivity value of 1010 cm Hz1/2/W at a temperature of 150 K and a wavelength of 42 μm The possibility to sense pulses of long-IR radiation by means of the PbTe diode was also demonstrated over the 100–180 K temperature range For the first time, a two-photon absorption-caused photovoltaic effect was observed in PbTe at a wavelength of 95 μm at 150 K

Excited state dynamics in a sodium and iodine co-doped lead telluride nanowire

Abstract: Materials that convert wasted heat into electricity are needed to help solve global warming and other climate challenges. Thermoelectric nanowires are novel metamaterials for such applications. Non...

Synergistic Strategies to Boost Lead Telluride as Prospective Thermoelectrics

Abstract: Lead telluride PbTe is a typical mid-temperature thermoelectric (TE) material, which has been intensively studied to achieve higher TE performance. We summarize three strategies that have been successfully applied in PbTe-based TE materials. The first strategy is charge carriers concentration engineering to optimize electrical transport. The optimal hole concentration for p-type PbTe is equal to (3–40) × 1019 cm−3, while for n-type PbTe, electron concentration is equal to (4–40) × 1018 cm−3, which is one order of magnitude lower than p-type. The second strategy is band engineering to enhance Seebeck coefficient. This strategy comprises band convergence, DOS distortion, resonant state, band alignment, band flattening, and impurity level. The third strategy is structural-defect engineering to lower the lattice thermal conductivity. In this part, the defects are sorted by dimensions from three-dimension to zero-dimension. At the end of the chapter, we give conclusion and prospects toward the PbTe system.

Morphology of Melt-Quenched Lead Telluride Single Crystals

Abstract: Metastable single crystals of nonstoichiometric Pb1-xTe are obtained by rapid cooling from the melt. The composition and crystallographic morphology are studied using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction. Most single crystals have cubic, pyramidal, or hemispherical shapes with sizes ranging from 50 to 400 μm. All crystals adopt the same face-centered cubic rock salt structure, and the crystal growth direction is ⟨100⟩. The bulk part of the rapidly cooled material solidifies in the form of a Te-rich polycrystalline material in which grains are separated by the PbTe-Te eutectic phase. The stabilization of nonstoichiometric Pb1-xTe provides further scope for the optimization of lead telluride-based thermoelectric materials.