PbTe Nanoparticles Research Articles

Defect mediated structural, optical, electrical and mechanical properties of mechano-synthesized PbTe nanostructure as a superior thermoelectric material: Correlation among electrical, mechanical and optical properties

This work reports on the formation of anti-site defects in mechanically alloyed PbTe samples and their anomalous effects on the optical and electrical properties of the sample. PbTe nanoparticles have been synthesised by mechanical alloying of the elemental Pb and Te powders mixed in stoichiometric ratio under an inert (Ar) atmosphere for different time durations. The structural and microstructural characterisations have been carried out by analysing X-ray diffraction (XRD) patterns, field-emission scanning electron microscope (FESEM), and high-resolution transmission electron microscope (HRTEM) images. The elemental composition has been revealed from the energy-dispersive X-Ray (EDX) spectrum. The phase pure cubic PbTe is formed within just 30 min of milling. The Rietveld analysis of XRD patterns, FESEM, and HRTEM images revealed the crystallite size reduction and the increase in r.m.s. lattice strain with the increase in milling durations. Inclusions of more and more anti-site defects of type [PbTe] with increasing milling time are reflected in the expansion of the cubic lattice parameter with milling durations. Fourier-transform infrared (FTIR) spectrum reveals that PbTe is a narrow bandgap semiconductor, and the bandgap shows a redshift with increased milling time and reduced crystallite size. This anomalous behaviour of the optical bandgap with reduced particle size is well explained by Urbach tailing due to increased defects in the more extended milled sample. The positions of the conduction and valence bands in the milled PbTe samples are determined for different milling times. The DC conductivity study also shows anomalous behaviour; electrical conductivity increases with particle size reduction in more extended milling time samples. It is resolved by considering that the carrier concentration increases with a longer milling time due to induced anti-site defects while milling. It results in bandgap reduction with milling durations and shows the predominant effect of electronic conductivity over ionic conductivity. The conduction mechanism is explained as per the Pertritz model, and the dependence of activation energies on particle size and temperature has been explained in detail. The Vickers hardness of the milled samples is determined, and its variation with grain size is explained with the Hall-Petch relation. The improved electrical conductivity with increased milling is also manifested in the measured hardness values.

In Situ Observation of Electron-Beam-Induced Formation of Nano-Structures in PbTe.

Nano-scaled thermoelectric materials attract significant interest due to their improved physical properties as compared to bulk materials. Well-shaped nanoparticles such as nano-bars and nano-cubes were observed in the known thermoelectric material PbTe. Their extended two-dimensional nano-layer arrangements form directly in situ through electron-beam treatment in the transmission electron microscope. The experiments show the atomistic depletion mechanism of the initial crystal and the recrystallization of PbTe nanoparticles out of the microparticles due to the local atomic-scale transport via the gas phase beyond a threshold current density of the beam.

Nanoarchitectonics of p-type BiSbTe with improved figure of merit via introducing PbTe nanoparticles.

Bi0.4Sb1.6Te3 (BST) is known to be a unique p-type commercial thermoelectric (TE) alloy used at room temperatures, but its figure of merit (ZT) is relatively low for wide industrial applications. To improve its ZT value is vitally important. Here, we show that the incorporation of 0.5 wt% PbTe nanoparticles into BST concurrently causes a large enhancement of power factor (PF) and a significant reduction of lattice thermal conductivity κL. The increase in PF mainly benefits from the optimization of carrier concentration, maintenance of high carrier mobility and constant rise in Seebeck coefficient. The decrease in κL can be attributed to the enhanced phonon scattering by the dispersed PbTe nanoparticles and the interfaces between PbTe and the BST matrix by using the Callaway model. Specifically, an ultralow κL of 0.26 W m−1 K−1 at 429 K is achieved for the composites incorporating 0.5 wt% PbTe nanoinclusions. Consequently, an excellent ZT = 1.6 at 482 K and a high average ZTave = 1.38 at 300–500 K are achieved, indicating that incorporation of PbTe in BST is an effective approach to improve its thermoelectric performance.

Enhancing the thermoelectric properties of SnTe via introducing PbTe@C core-shell nanostructures.

SnTe is an emerging IV-VI metal chalcogenide, but its low Seebeck coefficient and high thermal conductivity mainly originating from the high hole concentration limit its thermoelectric performance. In this work, an amorphous carbon core-shell-coated PbTe nanostructure prepared by a "bottom-up" method is first incorporated into the Sn1-ySbyTe matrix to enhance the thermoelectric performance of SnTe. The square-like PbTe nanoparticles maintain their original cubic morphology and do not grow up obviously after the SPS process due to the coating of the C layer, bringing about the formation of nanopores locally, while Sb alloying induces Sb point defects and Sb-rich precipitates. All these unique hierarchical microstructures finally lead to an ultralow lattice thermal conductivity (∼0.48 W-1 m-1 K-1) approaching amorphous limits (∼0.40 W-1 m-1 K-1). In addition, the incorporation of PbTe@C core-shell nanostructures decreases the carrier mobility obviously with a slight loss in carrier concentration, resulting in the deterioration of electrical properties to a certain extent. As a result, a peak thermoelectric figure of merit (ZT) of 1.07 is achieved for Sn0.89Sb0.11Te-5%PbTe@C at 873 K, which is approximately 154.76% higher than that of pristine SnTe. This work provides a new strategy to enhance the thermoelectric performance of SnTe and also offers a new insight into other related thermoelectric systems.

Effectiveness of undoped and (Nd, Yb)-doped PbTe nanoparticles deposition on supercapacitor performance of TiO2 nanotube arrays

Undoped and doped PbTe nanoparticles with neodymium (Nd) and ytterbium (Yb) ions were hydrothermally synthesized and deposited on anodized TiO2 nanotube (TNT) arrays to form hybrid binder-free TNT electrodes for supercapacitor. The as-prepared TNT electrodes were characterized by XRD, SEM, and XPS. Besides, BET method was used to confirm the surface area of as-synthesized nanoparticles. Among TNT electrodes, the one with Yb-doped PbTe exhibited enhanced capacitance (0.93 mF/cm2 at 10 mV/s, 2.16 mF/cm2 at 5 µA/cm2) and low resistance (4.68 Ω), along with good stability (~93%). Overall, TNT in combination with Yb-doped PbTe nanoparticles could provide an ideal platform for efficient delivery of capacitance.

Structural properties of PbTe quantum dots revealed by high-energy x-ray diffraction

High-energy x-ray diffraction (HE-XRD) experiments combined with an analysis based on atomic-pair-distribution functions can be an effective tool for probing low-dimensional materials. Here, we show how such an analysis can be used to gain insight into structural properties of PbTe nanoparticles (NPs). We interpret our HE-XRD data using an orthorhombic Pnma phase of PbTe, which is an orthorhombic distortion of the rocksalt phase. Although local crystal geometry can vary substantially with particle size at scales below 10 nm, and for very small NPs the particle size itself influences x-ray diffraction patterns, our study shows that HE-XRD can provide a unique nano-characterization tool for unraveling structural properties of nanoscale systems.

Colloidal quasicrystals based on hybrid nanoparticles

We used laser ablation approach for the synthesis of PbTe nanoparticles (NPs) that allows for the control of the mean size of NPs. The addition of gold particles to the solution results in the formation of hybrid NPs characterized by the amplification and broadening of the near-field photoluminescence spectra compared to initial NPs.

Lead Chalcogenide Nanoparticles and Their Size-Controlled Self-Assemblies for Thermoelectric and Photovoltaic Applications

We report a facile, room temperature synthesis of PbS, PbSe, PbSxSe1–x, and PbTe nanoparticles and their microscale assemblies by combining a chalcogen solution and a lead halide solution in select thiol–amine mixtures. Selection of an appropriate thiol–amine pair and/or the use of appropriate amine to thiol ratio has demonstrated a size control on nanoparticle self-assemblies ranging from nano- to microscale. Proper washing of these particles has yielded phase-pure and compositionally uniform material with minimal or no presence of any carbonaceous ligands on the particle surface, making it attractive for electronic device fabrication. The resulting PbS material exhibits bandgaps in the range 0.6 eV to as high as 1.2 eV for various assembly sizes. These optical bandgaps confirm the retention of quantum confinement of PbS material even in self-assembled nano/microstructures, which could be an interesting phenomenon for future photovoltaic development. Along with carbon-free, quantum-confined self-assemblies, this chemistry also provides a room temperature and instantaneous reaction route to synthesize individually dispersed PbS and PbSe particles with long chain ligand capping similar to traditional synthesis routes. The PbSe material synthesized from this route shows the ability to alloy with PbS at room temperature in the entire composition range and also demonstrates thermoelectric performance comparable to results in existing undoped PbSe literature.

Controlling dissolution of PbTe nanoparticles in organic solvents during liquid cell transmission electron microscopy.

We present direct visualization of the dynamics of oleic-acid-capped PbTe nanoparticles suspended in different organic solvents using liquid cell transmission electron microscopy. Liquid cell transmission electron microscopy is a powerful tool to directly observe the behavior of a variety of nanoparticles in liquids, but requires careful consideration and quantification of how the electron beam affects the systems being investigated. We find that etching and dissolution of PbTe nanoparticles occurs with a strong dependence on electron dose rate ranging from no perceivable effect on the nanoparticles with lower dose rates (50 e- Å-2 s-1) to complete dissolution within seconds or minutes at higher dose rates (100 and 200 e- Å-2 s-1). We propose that oxidative etching, resulting from the radiolysis of small amounts of water, causes the PbTe nanoparticles to dissolve after exposure to a threshold electron dose rate of 50 e- Å-2 s-1.

Application of Aqueous-Based Covalent Crosslinking Strategies to the Formation of Metal Chalcogenide Gels and Aerogels

Abstract An aqueous-based metal ion crosslinking approach for assembly of metal chalcogenide nanoparticles (NPs) into robust gels is reported. Short chalcogenide ligands (S2−) undergo crosslinking with metal salts (Sn4+) to form a gel [NP/S2−/Sn4+]n (NP=PbTe, PbS, CdS, CdSe). The corresponding aerogel networks retain the crystallinity and quantum confinement effects of the native building blocks while achieving excellent porosity [Brunauer–Emmett–Teller (BET) surface areas of 160–238 m2/g]. Treatment of sulfide-capped PbTe nanoparticles with an excess of Sn4+ leads to ion exchange and formation of an amorphous “SnTe” gel.

An Unconventional Route to Monodisperse and Intimately Contacted Semiconducting Organic–Inorganic Nanocomposites

We developed an unconventional route to produce uniform and intimately contacted semiconducting organic-inorganic nanocomposites for potential applications in thermoelectrics. By utilizing amphiphilic star-like PAA-b-PEDOT diblock copolymer as template, monodisperse PEDOT-functionalized lead telluride (PbTe) nanoparticles were crafted via the strong coordination interaction between PAA blocks of star-like PAA-b-PEDOT and the metal moieties of precursors (i.e., forming PEDOT-PbTe nanocomposites). As the inner PAA blocks are covalently connected to the outer PEDOT blocks, the PEDOT chains are intimately and permanently tethered on the PbTe nanoparticle surface, thereby affording a well-defined PEDOT/PbTe interface, which prevents the PbTe nanoparticles from aggregation, and more importantly promotes the long-term stability of PEDOT-PbTe nanocomposites. We envision that the template strategy is general and robust, and offers easy access to other conjugated polymer-inorganic semiconductor nanocomposites for use in a variety of applications.

An Unconventional Route to Monodisperse and Intimately Contacted Semiconducting Organic–Inorganic Nanocomposites

AbstractWe developed an unconventional route to produce uniform and intimately contacted semiconducting organic–inorganic nanocomposites for potential applications in thermoelectrics. By utilizing amphiphilic star‐like PAA‐b‐PEDOT diblock copolymer as template, monodisperse PEDOT‐functionalized lead telluride (PbTe) nanoparticles were crafted via the strong coordination interaction between PAA blocks of star‐like PAA‐b‐PEDOT and the metal moieties of precursors (i.e., forming PEDOT–PbTe nanocomposites). As the inner PAA blocks are covalently connected to the outer PEDOT blocks, the PEDOT chains are intimately and permanently tethered on the PbTe nanoparticle surface, thereby affording a well‐defined PEDOT/PbTe interface, which prevents the PbTe nanoparticles from aggregation, and more importantly promotes the long‐term stability of PEDOT–PbTe nanocomposites. We envision that the template strategy is general and robust, and offers easy access to other conjugated polymer–inorganic semiconductor nanocomposites for use in a variety of applications.

Aberration Corrected STEM Study of the Surface of Lead Chalcogenide Nanoparticles

In this contribution, we report on the microscopic and spectroscopic characterization of lead chalcogenide nanoparticles. PbSe and PbTe nanoparticles were synthesized by chemical methods, using different molar ratios of Pb, Se, and Te precursors and varying the reaction time. These nanoparticles were characterized by means of transmission electron microscopy and their related techniques: electron diffraction, energy dispersive X-ray spectroscopy (EDXS), electron energy loss spectroscopy (EELS), and aberration corrected scanning transmission electron microscopy (AC-STEM), to obtain information related to their morphology, crystal structure, and composition. They were also characterized by means of Fourier transform infrared (FTIR) absorption spectroscopy to assess the functional groups found on the surface of the nanoparticles, depending on the synthesis conditions. The results obtained showed that the synthesized nanoparticles always display a higher concentration of Pb compared to that of the chalcogen. ...

Synthesis and application of lead telluride nanoparticles for degrediation of organic pollution

PbTe nanoparticles were achieved from reaction of Pb(NO)3 and TeCl4 (as a new precursor for Tellur) in a relatively short time and low temperature in a hydrothermal process. The photocatalytic behavior of nanoparticles was evaluated using the degradation of a methyl orange (MeO) aqueous solution (as an organic pollution) under ultraviolet (UV) light irradiation. The results confirm that nanoparticles are promising materials with excellent performance in photocatalytic applications. In addition to, observations suggest that the as-obtained PbTe nanoparticles exhibit a strong PL peak at room temperature that might be ascribed to the high level transition in the PbTe semiconductor.

Synthesis of Cadmium and Lead Telluride Nanoparticles: Examples of Oriented attachment Growth Mechanism

ABSTRACTThe synthesis of hexadecylamine capped (HDA) CdTe and PbTe via a simple hybrid solution based high temperature route is described. In this method the tellurium is first reduced to form the telluride salt followed by reaction with the metal salt and finally thermolysis in a coordinating solvent. The metal salt and reaction temperature played an important role in the morphology and growth mechanism of the particles. The CdTe particles where in the form of rods and spheres whereas the PbTe nanoparticles were in the form of nanowires. The oriented attachment mechanism is proposed for the growth of elongated particles under certain reaction conditions.

Pressure-Induced Switching between Amorphization and Crystallization in PbTe Nanoparticles

Combining in situ high-pressure X-ray scattering with transmission electron microscopy, we investigated the pressure-induced structural switches between the rock salt and amorphous phases as well as the associated mechanisms of their crystallization and growth in 6 nm PbTe nanocrystal. It was observed that rock salt PbTe nanocrystal started to become amorphous above 10 GPa and then underwent a low-to-high density amorphous phase transformation at pressures over 15 GPa. The low-density amorphous phase exhibited a structural memory of the rock salt phase, as manifested by a backward transformation to the rock salt phase via single nucleation inside each nanoparticle upon the release of pressure. In contrast, the high-density amorphous phase remained stable and could be preserved at ambient conditions. In addition, electron beam-induced heating could drive a recrystallization of the rock salt phase on the recovered amorphous nanoparticles. These studies provide significant insights into structural mechanisms for pressure-induced switching between amorphous and crystalline phases as well as their associated growth processes.

On the role of Pb0 atoms on the nucleation and growth of PbSe and PbTe nanoparticles

In this contribution, a nucleation and growth mechanism of PbSe and PbTe nanoparticles are proposed. The formation and growth of PbSe and PbTe nanoparticles during their reaction synthesis were studied and followed using transmission electron microscopy, and their related techniques. In the synthesis method, trioctylphosphine-selenide and telluride were used as the chalcogen precursors, while lead oleate was employed as the lead precursor. Different synthesis conditions were tested to assess the effect of varying the reaction time, lead to chalcogen ratio, reaction temperature, and lead oleate concentration. The synthesized nanoparticles were characterized by means of electron diffraction, energy dispersive X-ray spectroscopy, scanning transmission electron microscopy, and electron energy loss spectroscopy, to obtain information related to their morphology, crystal structure, and composition. The experimental results suggest that the growth of the lead chalcogenide nanoparticles greatly relies on the reduction of Pb2+ ions to Pb0 atoms at early reaction times; this reduction of the lead precursor is evidenced by the formation of Pb nanoparticles with sizes between 1 and 3 nm under certain synthesis conditions. These Pb nanoparticles gradually disappear as the reaction progresses, suggesting that the reduced Pb0 atoms are able to contribute to the growth of the PbSe and PbTe nanoparticles, reaching sizes between 8 and 18 nm. The current results contribute to a better understanding of the nucleation and growth mechanisms of lead chalcogenide nanoparticles, which will enable the definition of more efficient synthesis routes of these types of nanostructures.

In situ synthesis and thermoelectric properties of PbTe–graphene nanocomposites by utilizing a facile and novel wet chemical method

In this work, a facile and novel wet chemical method is adopted to synthesize PbTe–graphene nanocomposites, and the thermoelectric properties of the sintered bulk materials are discussed in detail. An intercalative nanostructure is formed by using commercial graphene oxide nanosheets as both the dispersant and the two-dimensional growth template for PbTe nanoparticles in the synthesis process, where PbTe nanoparticles are in situ synthesized and graphene oxide nanosheets are reduced to graphene at the same time. FESEM and TEM measurements indicate that PbTe nanoparticles with sizes of 20–60 nm are uniformly anchored on the surface of graphene, and the nanostructure is retained in the bulk. These novel nanocomposites show enhanced thermoelectric properties as compared to bare PbTe prepared by the same route, as well as to samples prepared by traditional methods. The ultra-high electron mobility of graphene improves the electrical conductivity of the PbTe–graphene nanocomposites, and their conductivity exceeds not only that of bare PbTe but also the samples prepared by the traditional melt-quenching and melt-cooling processing techniques. Moreover, the much-decreased size of the PbTe particles in the bulk material, caused by the intercalative structure, increases the concentration of interfaces which results in the thermal conductivity of the nanocomposite being lower compared with the bare PbTe sample. Therefore, a much higher ZT value of the PbTe–graphene nanocomposites is obtained, reaching a value of 0.7 at 670 K. This is 6 times the value of the bare PbTe sample and a significantly higher ZT than for any n-type PbTe samples prepared by any of the traditional synthesis routes.

Sign changes of seebeck coefficients due to extrinsic-to-intrinsic transition for PbTe nanocrystals

Three types of PbTe samples, e.g. nanoparticles, nanowires and bulk ingots, have been prepared. The investigation of the Seebeck coefficient of PbTe nanoparticles and nanowires clearly shows the sign change in the temperature range of 575~650 K, which is not observed for bulk ingots. Unfortunately, this temperature range is within the proposed operation temperature range for thermoelectric devices using PbTe and hence, such a change will affect their proper performance. The observed sign change of Seebeck coefficient is not simply caused by the composition variation at high temperature. It is mainly attributed to the extrinsic-to-intrinsic-semiconductor transition for PbTe nanocrystals due to the competing factors between quantum size effect increasing band gap and self-purification process decreasing their charge carrier concentration, which shift the transition point of nanocrystals to lower range as compare to that of bulk samples. Thus, such phenomenon should be considered carefully in the design of thermoelectric devices using semiconductor nanocrystals, which have attracted much attention recently.

Sonoelectrochemical synthesized RGO–PbTe composite for novel electrochemical biosensor

Abstract Reduced graphene oxide–lead tellurium (RGO–PbTe) composites were fabricated via sonoelectrochemical technique. The crystalline structure, composition and morphology of the products were characterized by X-ray powder diffraction (XRD), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM), respectively. The results showed that the PbTe nanoparticles (NPs) were uniformly decorated on the RGO sheets. The formation mechanism of RGO–PbTe nanocomposite was proposed. Ultrasonic played an important role in the formation of PbTe NPs. The composites were further used as supports for immobilization of hemoglobin (Hb) to fabricate a novel electrochemical biosensor, which had good thermal stability, conductivity and biocompatibility and enhanced direct electron transfer. This biosensor showed excellent electrocatalytic activity towards H 2 O 2 with a linear range from 0.5 to 30 μM and low detection limit as 0.13 μM.