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Most achievements on remarkable thermoelectric performance have been made in the intermediate-temperature p-type PbTe. However, the n-type PbTe exhibits a relatively poor figure of merit ZT, which is urgently expected to be enhanced and compatible with the p-type counterpart. Here, we report that the introduction of excessive Pb can effectively eliminate cation vacancies in the n-type Pb 1 + x Te − 0.4 % I , leading to a considerable improvement of carrier mobility μ. Moreover, further Ge doping induces a large enhancement of thermoelectric properties due to the combined effect of improved electrical transport properties and increased phonon scattering in the n-type Pb 1.01 Te − 0.4 % I − y % Ge. The Ge doping not only contributes to the increase of the Seebeck coefficient owing to the increased effective mass m ∗ , but also gives rise to the dramatic decrease of lattice thermal conductivity due to the strengthened point defects scattering. As a result, a tremendous enhancement of the ZT value at 723 K reaches ∼ 1.31 of Pb 1.01 Te − 0.4 % I − 3 % Ge. Particularly, the average Z T a v e value of ∼ 0.87 and calculated conversion efficiency η ∼ 13.5 % is achieved by Ge doping in a wide temperature range from 323 to 823 K. The present findings demonstrate the great potential in the n-type Pb 1.01 Te − 0.4 % I − y % Ge through a synergistic tuning of carrier mobility, effective mass, and point defects engineering strategy. [ABSTRACT FROM AUTHOR]

Boltzmann transport calculations based on band structures generated with the density functional theory are often used in the discovery and analysis of thermoelectric materials. In standard implementations, such calculations require dense k-point sampling of the Brillouin zone and are therefore typically limited to the generalized gradient approximation (GGA), whereas more accurate methods such as hybrid functionals would have been preferable. GGA variants, however, generally underestimate the band gap. While a premature onset of minority carriers can be avoided with scissor corrections, the band gap also affects the band curvature. In this study, we resolved the k-point sampling issue in hybrid-functional based calculations by extending our recently developed k · p ̃ interpolation scheme [K. Berland and C. Persson, Comput. Mater. Sci. 134, 17 (2017)] to non-local one-electron potentials and spin-orbit coupling. The Seebeck coefficient generated based on hybrid functionals was found to agree better than GGA with experimental data for GaAs, InP, and PbTe. For PbTe, even the choice of hybrid functional has bearing on the interpretation of experimental data, which we attribute to the description of valley convergence of the valence band. [ABSTRACT FROM AUTHOR]

A systematic study of structural, microstructural, and thermoelectric properties of bulk PbTe doped with indium (In) alone and co-doped with both indium and iodine (I) has been done. X-ray diffraction results showed all the samples to be of single phase. Scanning electron microscopy (SEM) results revealed the particle sizes to be in the range of micrometers, while high resolution transmission electron microscopy was used to investigate distinct microstructural features such as interfaces, grain boundaries, and strain field domains. Hall measurement at 300K revealed the carrier concentration ~1019cm-3 showing the degenerate nature which was further seen in the electrical resistivity of samples, which increased with rising temperature. Seebeck coefficient indicated that all samples were n-type semiconductors with electrons as the majority carriers throughout the temperature range. A maximum power factor ~25 µW cm-1 K-2 for all In doped samples and Pb0.998In0.003Te1.000I0.003 was observed at 700 K. Doping leads to a reduction in the total thermal conductivity due to enhanced phonon scattering by mass fluctuations and distinct microstructure features such as interfaces, grain boundaries, and strain field domains. The highest zT of 1.12 at 773K for In doped samples and a zT of 1.1 at 770K for In and I co-doped samples were obtained. [ABSTRACT FROM AUTHOR]

The microstructure of polycrystalline PbTe1-xSex-ZnSe composite thin films has been studied by scanning transmission electron microscopy and electron diffraction. The films were prepared by the one-step synthesis method using simultaneous evaporation of PbTe and ZnSe. The nanocrystals of PbTe1-xSex are formed in a ZnSe matrix. Tellurium concentration can be tuned by controlling the PbTe evaporation source temperatures between 753K and 793 K. Binary PbSe nanocrystals were formed at 753 K, while ternary PbTe1-xSex nanocrystals were formed at 793 K. The nanocrystals grow in a granular shape at the initial stage of film growth, and the morphology changes to nanowire-shape as the film grows, irrespective of the Te concentration. The ternary PbTe1-xSex nanocrystals were composed of two phases with different Te concentration; Te-rich (Se-poor) granular crystals were formed near the bottom half parts of the film and Te-poor (Se-rich) nanowires were formed at the upper half parts of the film. Columnar ZnSe crystals contain high-density {111} stacking faults due to the low stacking fault energy of ZnSe. A balance of deposition and reevaporation on the substrate during the film growth will be responsible for the resultant nanocrystal morphology. [ABSTRACT FROM AUTHOR]

In an attempt to reduce the reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of n-type Pb1-xTixTe alloys, with x values of up to 3%. A solubility limit of 0.5 at. % Ti in PbTe was identified, while beyond this composition, a precipitation of a TiTe2 phase was occurred. An impressive maximal dimensionless thermoelectric figure of merit ZT of ~1.2 was obtained upon 0.1% Ti doping at 500 °C, indicating a ~9% efficiency enhancement compared to an undoped PbTe. It is shown that generating a functionally graded material based on undoped PbTe as a low temperature segment and a 0.1% Ti doped PbTe as a high temperature segment has a potential to enhance the efficiency by ~14% compared to the undoped sample. [ABSTRACT FROM AUTHOR]

We study theoretically the effect of heavy doping on the thermoelectric properties of p-type PbTe in the acceptor doping interval of 5 × 1019 to 4 × 1020 cm−3 and in the temperature range of 300 to 900 K. In our calculations, a three-band model of the PbTe electron energy spectrum is used that takes into account not only the light electron and hole bands but also the heavy-hole band. This so-called Σ-band plays an important role in the emergence of the figure-of-merit increase in this material at heavy acceptor doping. The calculated thermoelectric characteristics appear to be sensitive to the doping level. An increase in the figure-of-merit up to ZT ≈ 1.3 at 900 K was found at the doping level of 2 × 1020 cm−3. The maximum of ZT on the temperature axis is situated close to the temperature at which the light hole and heavy hole band edges coincide and hence, a prominent density-of-states singularity appears in the valence band, and the Fermi level lies near this singularity. [ABSTRACT FROM AUTHOR]

We study the effect of nanoscale precipitates on lattice thermal conduction in thermoelectric PbTe using a combination of ab-initio phonon calculations and molecular dynamics. We take into account the effects of mass difference and change in force constants, and find an enhanced influence of the latter with increased precipitate concentration. As a consequence, our inclusion of the change in force constants in the calculation affords a smaller predicted optimal nano-precipitate size that minimizes the thermal conductivity. These results suggest that the phonon scattering by nanoprecipitates in thermoelectric composites could be stronger than previously thought. [ABSTRACT FROM AUTHOR]

Striving for improvements of the thermoelectric (TE) properties of the technologically important lead telluride (PbTe) compound, we investigate the influence of different doping elements on the thermal conductivity, Seebeck coefficient, and electrical conductivity applying density functional theory calculations. Our approach combines total-energy calculations yielding lattice vibrational properties with the Boltzmann transport theory to obtain electronic transport properties. We find that doping with elements from the 1st and 3rd columns of the periodic table reduces the sound velocity and, consequently, the lattice thermal conductivity, while 2nd column dopants have no such influence. Furthermore, 1.6 at.% doping with 4th and 5th column elements provides the highest reduction of lattice thermal conductivity. Out of this group, Hf doping results in maximum reduction of the sound velocity from 2030m s-1 for pure PbTe to 1370m s-1, which is equivalent to ca. 32% reduction of lattice thermal conductivity. The highest power factor values calculated for 1.6 at.% doping range between 40 and 56 μW cm-1 K-2, and are obtained for substitution with dopants having the same valence as Pb or Te, such as those located at the 2nd, 14th, and 16th columns of the periodic table. We demonstrate how this method may be generalized for dopant-selectionoriented materials design aimed at improving TE performance of other compounds. [ABSTRACT FROM AUTHOR]

In this work, we investigate the crystal anharmonic effects in the thermoelectric properties of ntype 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. [ABSTRACT FROM AUTHOR]

We determined the temperature effects on the electronic properties of lead telluride (PbTe) such as the energy bandgap and the effective masses of charge carriers by incorporating the structural changes of the material with temperature using ab-initio density functional theory (DFT) calculations. Though the first-principles DFT calculations are done at absolute zero temperatures, by incorporating the lattice thermal expansion and the distortion of Pb2+ ions from the equilibrium positions, we could determine the stable structural configuration of the PbTe system at different temperatures. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Undoped PbTe was melted at 1123 K, ball milled (BM) at rotation speeds from 90 to 180 rpm and hot pressed (HP) at 147 MPa and 650 K. Milling at 120 rpm produced the minimum phonon thermal conductivity of 1.29Wm-1K-1 and average grain size of 0.80 µm. Phonon thermal conductivity was constant from coarse grain size to fine grain size of 1 µm and decreased suddenly at 0.80 µm. This tendency of phonon thermal conductivity corresponded to theoretical calculations with grain boundary scattering. However, the observed critical point of 1 µm was much larger than the calculated value of 0.03 µm. There was a significant inverse relationship between phonon thermal conductivity and FWHM of X-ray diffraction peaks. The low phonon thermal conductivity was associated with not only grain boundary scattering but high internal strain. [ABSTRACT FROM AUTHOR]

The methodology for a heterodyned laser-induced transient thermal grating technique for non-contact, non-destructive measurements of thermal transport in opaque material is presented. Phase-controlled heterodyne detection allows us to isolate pure phase or amplitude transient grating signal contributions by varying the relative phase between reference and probe beams. The phase grating signal includes components associated with both transient reflectivity and surface displacement whereas the amplitude grating contribution is governed by transient reflectivity alone. By analyzing the latter with the two-dimensional thermal diffusion model, we extract the in-plane thermal diffusivity of the sample. Measurements on a 5 μm thick single crystal PbTe film yielded excellent agreement with the model over a range of grating periods from 1.6 to 2.8 μm. The measured thermal diffusivity of 1.3 × 10-6 m2/s was found to be slightly lower than the bulk value. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Theoretical calculations of the Seebeck coefficients of bulk PbTe and PbTe based superlattices were described in the framework of Boltzmann equation, taking into account temperature dependent band gaps, nonparabolicity, and anisotropy of effective masses. It is shown that the temperature gradient along the superlattice layer works more effectively on the enhancement of the thermoelectric figure of merit than the temperature gradient normal to the superlattice layer. Calculated Seebeck coefficients were compared to the experimental values for n-type PbTe, p-type PbTe, and EuTe/PbTe superlattices. The Seebeck coefficient of p-type PbTe was higher than that of n-type PbTe. The relatively high Seebeck coefficient is explained by the contribution from other extrema in the valence band. The EuTe/PbTe [001] superlattice shows higher Seebeck coefficients than PbTe bulk owing to the large density of states. [ABSTRACT FROM AUTHOR]

Nanocrystalline PbTe films are deposited on different substrates at room temperature through thermal evaporation. The films are stoichiometric single-phase polycrystalline with (200) texture. Electrical properties of the films are analyzed in the framework of a grain boundary channel conduction model. The index of refraction and extinction coefficient of PbTe films are extracted from infrared spectroscopic ellipsometry measurement in the wavelength range of 2–8 μm, yielding an optical band gap of 0.386 eV and evidence for the presence of an Urbach band tail. The optical band gap is larger than the typical value for bulk material due to quantum confinement effect. [ABSTRACT FROM AUTHOR]

Phonon modes of PbTe films grown by molecular beam epitaxy have been studied by micro-Raman scattering. On the as-grown PbTe surface, strong TeO2 phonon vibrational modes were detected, which obscured the observation of the longitudinal optical (LO) phonons of PbTe in early conventional Raman scattering experiments. Existence of a TeO2 layer on the PbTe surface is confirmed by observation with x-ray photoemission spectroscopy. After removal of TeO2 by chemical etching, the LO phonons for PbTe films were unambiguously observed. Misfit strain accommodated in the epitaxial films makes the lattice distorted from cubic structure, which lowers the crystal symmetry and leads to observation of what would normally be Raman inactive LO phonon modes for PbTe. [ABSTRACT FROM AUTHOR]

This article reviews recent developments in the physics of lead telluride nanostructures. PbTe is a IV–VI narrow gap paraelectric semiconductor, characterized by the huge static dielectric constant [variant_greek_epsilon]>1000 at helium temperatures. Methods of gating and nanostructure fabrication of modulation doped PbTe/Pb1-xEuxTe quantum wells are described. Specific properties of PbTe, make it possible to put into evidences a number of interesting effects in the quantum ballistic regime, not encountered in standard semiconductor nanostructures. It is found that conductance of narrow constrictions shows precise zero-field quantization in 2e2/h units, despite a significant amount of charged defects in the vicinity of the conducting channel. This unusual result is a consequence of a strong suppression of Coulomb potential fluctuations in PbTe, an effect confirmed by numerical simulations. Furthermore, orbital degeneracy of electron waveguide modes can be controlled by the width of PbTe/Pb1-xEuxTe quantum wells, so that unusual sequences of plateau conductance are observed. Finally, because of a rather large Zeeman splitting in PbTe, significant spin splitting of the conductance plateaus is observed already in the magnetic fields of about 0.2 T. It is shown that PbTe quantum wires act as efficient local spin-filters, in which the spin polarized current is carried by a large number of wire modes. [ABSTRACT FROM AUTHOR]

Lead telluride mesa diodes were fabricated from a series of p-n junctions grown on (111) BaF2 substrates, in which the hole concentration p was kept constant at 1017 cm-3 and the electron concentration n varied between 1017 and 1019 cm-3. Capacitance-voltage analysis showed that for n>1018 cm-3 the PbTe p-n junction is one sided and abrupt. The parameters (incremental resistance, series and parallel resistances, and ideality factor) obtained from the current-voltage (I-V) characteristics and the detectivity D* exhibited a large fluctuation among the photodiodes. In spite of these fluctuations, it was possible to correlate the noise and D* values to the parameters obtained from the I-V analysis. These results allow predicting the PbTe detector’s figures of merit from the data obtained from the I-V curves. The best PbTe photodiodes fabricated here showed D* values close to 1011 cm Hz1/2 W-1, comparable to InSb and HgCdTe commercial detectors and to PbTe sensors fabricated on Si substrates. [ABSTRACT FROM AUTHOR]

Presents information on study that created and examined nanometer scale features on the semiconductor p-PbTe single crystal surface by means of a scanning tunneling microscope. Experimental technique; Results and discussion; Conclusion.

Studies fast recombination processes in lead chalcogenide semiconductors via transient optical nonlinearities. Synopsis of the material properties of lead salt semiconductors; Material properties of lead chalcogenides; Stationary absorption of lead selenide and lead telluride crystals under normal incidence.

Deals with a series of studies which evaluated the growth and characterization of indium antimonide doped with lead telluride. Background to the study; Experimental procedures; Details of the transport studies; Results of the secondary-ion mass spectroscopy studies.

Presents study which examined bismuth- and thallium-doped lead telluride grown by molecular-beam epitaxy. Sample preparation; Results of scanning Auger electron spectroscopy; Results of ion mass spectroscopy.

Investigates the rotational weak-field magnetoresistance between 4.2 and 300 K on two doped lead telluride films. Experimental details; Use of neutron activation analysis and secondary mass spectroscopy to determine indium concentration; Summary and conclusions.

Thallium doping into lead telluride has been demonstrated to increase the dimensionless thermoelectric figure-of-merit (ZT) by enhancing Seebeck coefficient due to the creation of resonant states close to Fermi level without affecting the thermal conductivity. However, the process is tedious, energy consuming, and small in quantities since it involves melting, slow cooling for crystal growth, long time annealing, post-crushing and hot pressing. Here we show that a similar ZT value about 1.3 at 400 °C is achieved on bulk samples with grain sizes of 3–7 μm by ball milling a mixture of elemental thallium, lead, and tellurium and then hot pressing the ball milled nanopowders. [ABSTRACT FROM AUTHOR]

In this paper we report the observation of photothermal effect in PbTe p-n junction. The effect is expressed in photosignal generation due to illumination by 100 ns pulse CO2 laser with photon energy less than PbTe forbidden gap. [ABSTRACT FROM AUTHOR]

Abstract Single crystalline PbTe samples are prepared by the Pb-flux method according to the stoichiometric ratio of Pb 1+ x Te (x = 1.5, 2.0, 2.5, and 3.0). Experimental results show that all the samples exhibit n-type conductivity. The order of magnitude for carrier concentration is 1019, which is one order of magnitude higher than that in pure n-type PbTe sample (2.56 × 1018 cm−3). The highest power factor reaches 2.07 × 10−3 W m−1 K−2 at 420 K for the sample with x = 1.5, which is an approximately 30% enhancement compared with the polycrystalline sample (1.59 × 10−3 W m−1 K−2). In a theoretical study on the PbTe system, Te vacancy (V Te) is preferentially formed under the Pb-rich condition. To further understand the effect of V Te on the electrical performance of PbTe thermoelectric material, the electronic structures of PbTe with V Te are determined by first principle calculations. Theoretical calculations reveal that V Te can modify the electronic density of states by introducing resonant level, which can increase the number of carrier pockets. Consequently, carrier concentration has increased remarkably. In this study, a Pb-flux method for synthetizing single crystalline PbTe thermoelectric material is convenient and low cost, and it has potential for mass production in commercial applications. Highlights • Single crystalline PbTe samples were prepared by the Pb-flux method. • Carrier concentration was improved significantly. • Power factor was enhanced significantly compared with polycrystalline PbTe. • Effect of V Te on electrical performance was investigated by first principle. [ABSTRACT FROM AUTHOR]

Abstract Sputtering of PbTe, SnTe and GeTe compounds having both small and large differences in the individual components’ masses by Ar+ plasma under Secondary Neutral Mass Spectrometry (SNMS) conditions are investigated. The effect of preferential sputtering and its peculiar features caused by the different ratios between masses of the IVB atoms and tellurium were observed. The method and the empirical relationships for determination of the relative detection factor (RDF) of the intrinsic components of the compounds are suggested. It is shown that RDF of Te and metal species of the investigated samples isn’t a constant, but depends on sputtering energy. These dependences are explained by the changes of the sputtering surface morphology and the impact of mass of the sputtered species on the fraction of the species flux ejected into the solid angle collected by the spectrometer mass analyzer. The limits of applicability of SNMS for quantitative analysis of composite samples with big differences in masses of their constituents are established. A possible solution for such cases is proposed. It is shown that in the sequence of PbTe-SnTe-GeTe compounds the surface binding energy of the metal components decreases in the direction from lighter to heavier atom. [ABSTRACT FROM AUTHOR]

Abstract: Topological materials boast exotic metallic surface states with linear dispersion and spin‐momentum locking, which makes them potential candidates for dissipationless electronic and spintronic devices. Here, it is theoretically predicted that intrinsic Te antisite defects (TePb) in the narrow‐gap semiconductor PbTe induce a band inversion, turning it into a topological crystalline insulator (TCI). To experimentally verify the exotic properties, TePb antisites are introduced into PbTe crystals via nonstoichiometric growth by molecular beam epitaxy. Semimetallic resistivity and distinct quantum oscillations are observed on the TePb doped PbTe. Most importantly, a π Berry phase is unambiguously revealed by a Landau index analysis, demonstrating the Dirac fermion nature of the topological surface states. The discovered TCI nature in TePb doped PbTe is further explored using magneto‐transport measurements under external pressure, and the theoretical calculations of band structures with applying pressure indicate a pressure‐induced Lifshitz transition. Besides, it is proposed that the contribution of bulk states to transport can be reduced by enlarging the inverted gap with strain. [ABSTRACT FROM AUTHOR]

We create precursors for PbTe, PbSe, SnTe, and SnSe by reacting Pb or Sn with diphenyl dichalcogenides in a variety of different solvents. We then deposit PbSexTe1−x thin films using these precursors and measure their thermoelectric properties. Introducing Na-dopants into the films allows the thermoelectric properties to be varied. [ABSTRACT FROM AUTHOR]

Multilayer growth of an immiscible material system is an example of a self-ordering process which results in nanostructures of various patterns. PbTe and CdTe produce an excellent example of an immiscible material system because, despite having nearly the same lattice constants, both components crystallize in different crystal structures - rock salt and zinc blende - respectively. In this report we adjust the kinetic Monte Carlo (kMC) model proposed in our previous publication [1] to the case of PbTe/CdTe multilayer structures formed of ultra-thin PbTe and CdTe layers. The morphology of the multilayers is revealed by transmission electron microscopy (TEM) and the morphological patterns are simulated using the kMC model, which takes into account bulk and surface diffusion. An important factor which determines the morphology of the PbTe/CdTe superlattices is a significant anisotropy of both the surface and the bulk diffusion. The simulations show that the shape, size and dimensionality of the emerging nanostructures strongly depend on the amount of deposited components and the growth rate. Since the amount of the deposited material plays an important role, the desorption process from the surface has to be considered. Our kMC model with adjusted parameters correctly reproduces all morphological details observed in real PbTe/CdTe nanostructures grown with different growth rates and composition ratios. Finally, we show that the growth rate may be used to control morphological transitions between different types of structures of given compositions. [ABSTRACT FROM AUTHOR]

ZnTe and PbTe nanocrystals with average radii of 2.42 and 4.25 nm, respectively, were grown in a fluorophosphate glass host. A strong quantum confinement effect was induced as a result of the blue shifted optical absorption due to the ZnTe and PbTe nanocrystals. Optical constants, like the refractive index (n), complex dielectric constant, dissipation factor (tan δ) and optical conductivity (σopt), were extracted from the experimental transmittance T(λ) and reflectance R(λ) data. Moreover, the presence of both the ZnTe and PbTe nanocrystals were confirmed by X-ray diffraction analysis, revealing cubic and hexagonal wurtzite structures, respectively. The results of the optical absorption spectra were confirmed by the similar nanocrystal radii identified using transmission electron microscopy and X-ray diffraction analyses. Raman analysis of the heat-treated glass sample confirmed that bands at 65 and 103 cm−1 are due to the longitudinal optical (LO) modes of PbTe NCs. Also, the band at 214 cm−1 is attributed to first harmonic or fundamental LO mode of ZnTe NCs. [ABSTRACT FROM AUTHOR]

Lead telluride films have been grown on Si (100) and BaF2 (100) substrates by a modified hot-wall method using a graphite reaction chamber. According to X-ray diffraction, X-ray microanalysis, and scanning electron microscopy characterization results, the average growth rate of PbTe films having compositions within the homogeneity range of lead telluride increases with increasing lead vapor partial pressure and decreases with increasing tellurium vapor partial pressure, independent of the nature of the substrate. The rate of PbTe film growth has been shown to be maximal in the initial stage of the process and decrease monotonically over time, independent of the nature of the substrate. Independent of the growth time, the average growth rate of the PbTe films on the Si (100) substrates is considerably higher than that on the BaF2 (100) substrates. Reflection high-energy electron diffraction data indicate that the texture of the PbTe films on Si (100) corresponds to the substrate orientation and that the misorientation angle of the mosaic blocks does not exceed 20°. On the BaF2 (100) substrates, we observe epitaxial PbTe film growth with the orientation relationship (100), [011] PbTe ║ (100), [011] BaF2. [ABSTRACT FROM AUTHOR]

A few millimeter-long lead telluride (PbTe) hollow nanofibers with thermoelectric properties was synthesized for the first time with high through manner via three-step sequential process of electrospinning, electrodeposition and cationic exchange reaction. As-synthesized electrospun Ag nanofibers with ultra-long aspect ratio of 10,000 were Te electrodeposited to obtain silver telluride nanotubes and underwent cationic exchange reaction in Pb(NO 3 ) 2 solution to obtain polycrystalline PbTe nanotubes with average diameter of 100 nm with 20 nm of wall thickness. Variation of the Ag-to-Pb ratio in the Ag x Te y -PbTe nanocomposites during the cationic exchange reaction enabled to control the thermoelectric properties of resulting 1D hollow nanofibers. The diameter of Ag nanofiber is the key factor to determine the final dimension of the PbTe nanotubes in the topotactic transformation and the content of Ag ion leads to the enhancement of thermoelectric properties in the Ag x Te y -PbTe nanocomposites. The synthesized 1D nanocomposite mats showed the highest value of Seebeck coefficient of 433  μ V/K (at 300 K) when the remained Ag content was 30%, while the power factor reached highest to 0.567  μ W/mK 2 for the pure PbTe nanotubes. The enhancement of thermoelectric properties and the composite crystallinity are elucidated with relation to Ag contents in the resulting 1D nanocomposites. [ABSTRACT FROM AUTHOR]

Dendritic PbTe microstructures were successfully obtained by a simple potentiostatic electrodeposition route from an electrolyte consisting of Pb(NO3)2, Na2TeO3 and HNO3 at room temperature. Different from Xiao's report (Electrochimica Acta, 2006, 52, 1101), in which the effects of the deposition potential and original concentrations of Pb and Te sources on the film composition and microstructure of PbTe obtained from an acidic nitrate bath were investigated, our research mainly focused on the discussion of the role of HNO3 in the formation of PbTe dendrites. Experiments uncovered that some experimental parameters, including the deposition potential, the time and the additive, only slightly affected the formation of PbTe dendrites in the presence of HNO3 at a certain concentration. Also, no PbTe dendrites were obtained under the same deposition conditions after HNO3 had been replaced by other strong acids such as HCl, H2SO4 and HClO4, implying that HNO3 played a crucial role in the formation of dendritic PbTe microstructures. Obviously, the present work is of great significance in directing the fast electrodeposition of dendritic PbTe microstructures in practical applications. [ABSTRACT FROM AUTHOR]

Sodium is widely used as a substituting element in p-type PbTe-based thermoelectric materials. In this work, two series of polycrystalline samples Pb1-yNayTe1-y/2 (total charge balance) and Pb1-xNaxTe (total charge nonbalance) were examined. Na has limited solubility for both of the series. The MAS 23Na NMR analysis of Pb1-xNaxTe series (for Pb0.98Na0.02Te sample after spark-plasma sintering, SPS) reveals only one Na signal, corresponding to Na atoms coordinated by six Te atoms, indicating substitution of Pb by Na without defects in the Te sublattice. In the Pb1-yNayTe1-y/2 series, clustering of Na atoms with reduced coordination by Te was observed. Additional heat treatment of these samples leads to the reorganization of the Na clusters in PbTe and their equilibration with the homogenized distribution of Na in the whole volume. The maximum ZT values of 1.4-1.6 at 760 K are established for both Pb1-xNaxTe and Pb1-yNayTe1-y/2 series. Upon long-time annealing at 873 K, reorganization and redistribution of Na atoms lead to the change in carrier concentration and, consequently, the thermoelectric properties for both series. [ABSTRACT FROM AUTHOR]

A compositionally graded alloy in the PbTe–Sb 2 Te 3 –Ag 2 Te system was fabricated by the Bridgeman method. In the sample obtained for analysis, the length of the graded area was of the order of several tens of nanometers. Its thermal effusivity was measured with a thermal microscope, which required sputtering of a Mo film on the surface of the sample. The measured values of thermal effusivity depended on the thickness of the Mo film. However, it was difficult to sputter the Mo film uniformly in the wide area. Even though a relatively large target was used in the sputtering apparatus on the laboratory scale, the thickness of the Mo film just under the center of the target was larger than that in other areas. In this study, the measured thickness of the Mo film was calibrated with a high degree of accuracy against the reference glass slide. The thermal effusivity of the PbTe–Sb 2 Te 3 –Ag 2 Te alloy was in the range of 400–800 Ws 0.5 m −2 K −1 . [ABSTRACT FROM AUTHOR]

Functionally graded (PbTe)1-x(SnTe)x ingots have been prepared by Bridgman crystal growth method for the first time. From SEM-EDX, the composition (x) of the ingot was found to increase smoothly from 10.6 to 25.4 along the direction of the growth. The gradual change in composition is shown to cause a decrease in band gap as crystallization proceeds, and to be accompanied by a change in carrier concentration. By a Potential-Seebeck microprobe (PSM), a smoothly varying Seebeck coefficient was measured along the growth direction of the sample at room temperature. High-temperature properties relevant for thermoelectric performance were measured and used to evaluate the potential of this system as a functionally graded high-temperature thermoelectric material. This study provides insight into understanding the complicated interplays of advanced crystal growth and physical properties, going beyond standard thermoelectric sample preparation approaches. [ABSTRACT FROM AUTHOR]

Modeling thermoelectric generator (TEG) performances plays an important role in guiding the design of TEGs to achieve better efficiency. However, a rigorous 1-D TEG modeling performance has not yet been conducted, which prevents reliable prediction of TEG performance. In this work, a detailed 1-D model has been developed to take into account temperature-dependent thermoelectric material properties, heat loss due to radiation and conduction, and Thomson effect. A Lead Telluride (PbTe) TEG was chosen as a sample module and the modeling results agree very well with the experimental results, which proves how powerful the presented detailed 1-D model can be used to predict and validate TEG experimental results. TEG power and efficiency were found to have a respective decrease of 10% and 31% from the simplified model at a temperature gradient of 570 K. While heat loss attributable to conduction and radiation were found to be small, the Thomson effect, which is often neglected, was found to significantly reduce TEG performances. The deep analysis enabled by the new model provides useful guidelines to improve the performance of TEGs. [ABSTRACT FROM AUTHOR]

The combination of feasible bottom-up hydrothermal synthesis is demonstrated to notably enhance thermoelectric performance of the PbTe matrix with different Se-doped contents. The instinct electrical properties are improved by annealing with reducing gas to achieve relatively high power factor. Furthermore, multi-scale hierarchical architecture is established together with the point defects and dislocations introduced by doping Se and the formation of nanoscale participates, couple with increased boundaries and a large grain size scale from 20 nm to 1.5 μm and, resulting in scattering an even broader frequency spectrum of phonon mean free path to reduce the lattice thermal conductivity effectively. Consequently, it plays an essential synergistic optimization to achieve a maximum ZT value of 0.98 at 625 K from the as-prepared n-type PbTe 1-x Se x (x = 0.06) alloys. This study provides a facile and low-cost method to fabricate multi-scale hierarchical architecture materials on a large scale with significant enhancement of thermoelectric performance. [ABSTRACT FROM AUTHOR]

In this work, thermoelectric properties of Bi and Sb atoms substituted PbTe material were predicted by Mott theory through electronic structure calculation. This calculation has been carried by the first-principles DV-Xα molecular orbital method based on Hartree-Fock-Slater approximation. The Pb 14 Te 13 , Pb 13 SbTe 13 and Pb 13 BiTe 13 small clusters with a cubic rocksalt structure ( Fm -3 m ; 225) were designed to be performed PbTe, Pb 0.75 Sb 0.25 Te and Pb 0.75 Bi 0.25 Te materials, respectively. The electronic structure showed that the high symmetry crystal structure, spin energy levels, partial spin density of states and electron charge density. The energy gap and Fermi level have been obtained from energy levels and density of state to be evaluated of electrical conductivity and Seebeck coefficient within Mott's theory predication. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Nano- & Electronic Physics is the property of Sumy State University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Nano- & Electronic Physics is the property of Sumy State University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this work, a comparison between the performance of two- and three-stage cascaded thermoelectric generator (TEG) devices is analyzed based on a prescribed maximum hot side temperature of 973 K, an imposed maximum heat input of 505 W, and a fixed cold side temperature of 473 K. Half-Heusler is used as a thermoelectric (TE) material in the top higher temperature stage and skutterudite as a TE in the bottom lower temperature stage for the two-stage structure. Lead telluride is added in the middle stage to form the three-stage structure. Based on the prescribed constraints, the two-stage cascaded TEG is found to produce a power output of 42 W with an efficiency of 8.3%. The three-stage cascaded TEG produces a power output of 51 W with an efficiency of 10.2%. The three-stage cascaded TEG produces 21% more power than the two-stage does; however, if the system complexity, mechanical robustness, manufacturability, and/or cost of three-stage cascaded TEG outweigh the 21% percent power production increase, the two-stage TEG could be preferable. [ABSTRACT FROM AUTHOR]

We have investigated the influence of substituting bismuth for lead in lead telluride. The material was nanostructured by mechanical alloying and compacted via short-term sintering or hot pressing. Synthesis of samples with substitution up to 6 at.% bismuth was carried out twice to ensure reproducibility. All relevant thermoelectric transport parameters were measured in a wide temperature range from 123 K or 173 K to 773 K. Two different techniques for measuring the electrical conductivity and Seebeck coefficient were used, one at low and the other at high temperature. Higher bismuth content of 4 at.% to 6 at.% was found to result in the best thermoelectric properties, with maximum ZT value of about 0.7 at 723 K for 4.0 at.% bismuth. The structure was examined in detail via x-ray diffraction analysis, Raman spectroscopy, and transmission electron microscopy. A key feature of the microstructure was the inhomogeneous distribution of bismuth in the lead telluride matrix and the occurrence of bismuth-rich regions on the nanoscale, related to remarkably increased carrier concentration and mobility. [ABSTRACT FROM AUTHOR]

Present study reveals an impact of annealing on the crystallization of InSe matrix in PbTe-InSe multilayer nanocomposite structures prepared using thermal evaporation technique. Cross sectional transmission electron microscopic image clearly shows that the PbTe nanocrystals (NCs) are embedded in InSe matrix layer. Atomic force microscopic analysis gives detailed surface morphology of single PbTe NCs layer on InSe matrix surface. The growth of PbTe NCs with elongated surface morphology was observed upon annealing and correlated with Ostwald ripening. The evaluation of amorphous to crystalline phase transformation corresponding to InSe was observed from X-ray diffraction upon annealing. The shift in optical absorption spectra attribute three dimensional quantum confinement effect of PbTe NCs embedded in InSe matrix and have compared with the theoretical predictions of Efros effective approximation model. The photoluminescence emission associated with InSe matrix and PbTe NCs were observed with respect to annealing temperatures and are discussed. [ABSTRACT FROM AUTHOR]

A complex of models for optimizing the design and operation modes of an automotive thermoelectric generator is developed within the proposed approach taking into account the influence of hydraulic resistance of the generator on the internal combustion engine. Several designs of generators for converting the thermal energy of exhaust gases (EGs) of internal combustion engines into electricity due to the Seebeck effect in semiconductor elements, which have different geometries of the continuous-flow part of the generator with different hydraulic resistances, are considered. Models for calculating the thermoelectric elements, gas heat exchanger, and automotive engine are considered jointly. Simulation is performed using the example of a VAZ-21126 engine, which demonstrated that up to 500 W of electric power can be obtained using semiconductor thermoelectric elements based on germanium and lead tellurides. [ABSTRACT FROM AUTHOR]

Se 90 Te 8 Pb 2 and Se 90 Te 4 Pb 6 compositions have been prepared in bulk and thin film forms. Transmittance and reflectance have been measured for the investigated films over the wavelength range (500–2500 nm). The studied films are transparent where no light absorbed or scattered at the longer wavelength region, while they are absorbing at shorter wavelengths. The optical constants have been determined from the analysis of the transmittance and reflectance data using Murmann , s exact equations. The observed decrease in refractive index (n) values with Pb content is attributed to the increase of polarizability with Pb addition. Analysis of refractive index data yields some important parameters. An increase of Pb content in the studied film samples enlarge the Urbach's energy E e values from 0.071 to 0.12 eV, which considered due to increase of the disorder defect localized states. These localized states arise due to the high difference in atomic radii of Te and Pb atoms. The optical transitions are found to be indirect with optical energy gap decreasing from 1.7 to 1.19 eV with increasing Pb content. The nonlinear optical susceptibility and the nonlinear refractive index are calculated from the obtained data and their dependence of Pb content is discussed as well. [ABSTRACT FROM AUTHOR]

The review of works devoted to the use of polishing etchant composition for chemical treatment of the PbTe and Pb1-xSnxTe solid solutions single crystals and methods for their processing. [ABSTRACT FROM AUTHOR]

A type of metal-semiconductor-metal (MSM) photodetector based on PbTe single-crystalline nanowires was prepared. I–V characteristics of the photodetector in the temperature range of 77–300 K were studied. Little dark current was achieved in MSM PbTe nanowire photodetector at low bias voltages due to the formation of back to back Schottky junctions between the PbTe nanowires and Au electrodes. The influences of light intensity, bias voltage, and temperature on the performance of PbTe nanowire photodetector were investigated. It was found that the photocurrent is linear to light intensity. The photosensitivity of the typical photodetector was about 50% and varied only slightly as a function of bias voltage. Moreover, this photodetector displayed a fast respond compared with nanoparticle photodetector due to the one dimensional structure and the high crystallinity of nanowires. [ABSTRACT FROM AUTHOR]