Thermoelectric Energy Conversion Efficiency Research Articles

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The quest for efficient thermoelectric materials has intensified with the advent of novel Janus monolayers exhibiting exceptional thermoelectric parameters. In this work, we comprehensively investigate the structural, electronic, transport, phonon, and thermoelectric properties of novel Janus γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-Pb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}XY (X=S, Se; Y=Se, Te; X≠\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ e $$\\end{document}Y) monolayers using density functional theory combined with the Boltzmann transport equation. Our findings unveil the energetic, dynamic, thermal, and mechanical stability of these monolayers, along with their remarkable thermoelectric performance. Remarkably, the p-type γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-Pb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}SeTe monolayer exhibits an outstanding figure of merit (ZT) of 6.88 at 800 K, attributed to its intrinsically low lattice thermal conductivity of 0.162 Wm-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document}K-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document} arising from strong phonon scattering, low group velocity, low phonon relaxation time, and a high Grüneisen parameter. Furthermore, these monolayers demonstrate high Seebeck coefficients and electrical conductivities, making them promising for efficient charge transport and thermoelectric energy conversion. Our results highlight the immense potential of Janus γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document}-Pb2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}XY monolayers as promising candidates for high-temperature thermoelectric applications and open up exciting avenues for further exploration of these novel two-dimensional materials in energy-related technologies.

Enhancing performance and thermal stability in GeTe thermoelectric joints with cobalt diffusion barrier

This study investigates the influence on thermoelectric properties of p-type GeTe after depositing cobalt (Co) diffusion barrier, and its ability on inhibiting the interfacial reactions that degrades thermoelectric performance of the joint at medium temperatures. Establishing stable interconnections within the joint is essential for ensuring the reliability of the device. By examining the improved thermoelectric properties of GeTe, the research highlights a discovering that the addition of a Co diffusion barrier significantly elevates figure of merit (zT) values of GeTe. Electron probe microanalysis (EPMA) reveals the diffusion of Co into GeTe and the formation of Co–Te intermetallic compounds. As the device ages, there is a substantial increase in contact resistivity at the GeTe joint. After depositing a Co layer and subjecting it to long-term aging, electrical conductivity improves, and thermal conductivity decreases. This improvement occurs because the Co atoms, which have diffused into the GeTe lattice, occupy Ge vacancy sites. Instead of degrading the zT value, Co deposition leads to a 56 % increase in the zT value for the p-type GeTe joint. This study emphasizes the improvement of the zT value rather than pursuing a high peak zT value for GeTe. These results affirm the role of Co as an effective diffusion barrier, contributing to the stability of the joint interface and the enhancement of the thermoelectric properties of GeTe material, offering a viable route for creating more efficient and durable thermoelectric energy conversion devices.

Non-monotonic variation of the thermoelectric efficiency with modulation mismatch in width-modulated nanowaveguides

Efficient thermoelectric energy conversion at the nanoscale could power the Internet of Things and cool nanoelectronic circuits and improve the performance of quantum applications. Width-modulated nanowaveguides are suitable for these purposes because their thermoelectric efficiency can be geometrically tuned and integrated into the nanoelectronics industry processes. They are attracting increasing research interest stimulated by theoretical predictions for exceptional performance. To validate their potential, a better understanding of the effect of width modulation on thermoelectric efficiency is needed. So far, it is considered that (a) the thermoelectric efficiency increases monotonically with increasing width-mismatch due to decreasing phonon thermal conduction taking place without significantly affecting electron transport, (b) width-mismatch dominates the effect of width modulation in transport, and (c) phonons play the main role in increasing the thermoelectric efficiency. Here, we demonstrate counterevidence based on an investigation of the effect of width modulation on electrons so far overlooked. We reveal that (a) the thermoelectric efficiency varies non-monotonically with the modulation mismatch due to quantum effects on electron transport, (b) the modulation mismatch is quantified by the size-mismatch of the modulation rather than by the width-mismatch, and (c) it is electrons rather than phonons that play the main role in optimizing width modulation for maximum thermoelectric efficiency when quantum effects dominate. Our findings indicate that research should reorient from large width-mismatch toward optimal modulation-mismatch width-modulated nanostructures to enhance thermoelectric efficiency due to quantum effects. Our work provides new insight for designing nanowaveguides for efficient thermoelectric energy conversion at the nanoscale.

Influence of the Anderson Transition on Thermoelectric Energy Conversion in Disordered Electronic Systems

So far, the efficiency of thermoelectric energy conversion remains low compared to traditional technologies, such as coal or nuclear. This low efficiency can be explained by connecting the thermoelastic properties of the electronic working fluid to its transport properties. Such connection also shows that operating close to electronic phase transitions can be an efficient way to boost the thermoelectric energy conversion. In this paper, we analyze themoelectric efficiency close to the metal-insulator Anderson transition. Our results reveal the direct link between the thermoelectric and thermoelastic properties of Anderson-type systems. Moreover, the role of the conductivity critical exponent in the thermoelectric energy conversion is analysed. Finally, we show that relatively large values of the thermolectric figure of merit may be obtained in the vicinity of the Anderson transition.

A promising high temperature 2D thermoelectric material: novel single-layer ZrHfS4.

Based on the first-principles calculation and Boltzmann transport theory, we report the discovery of a promising candidate for high-performance two-dimensional (2D) thermoelectric material: the single-layer (1L) ZrHfS4. Through the first-principles molecular dynamics simulation and phonon calculation, 1L-ZrHfS4 is predicted to be thermodynamically stable even at high temperatures. In addition, the lattice thermal conductivity of 1L-ZrHfS4 is calculated to be 10.2 W m-1 K-1, which is smaller than that of 2D transition-metal dichalcogenides, such as MoS2 and WS2. Notably, considering not only all the transport coefficients but also the relaxation time for both acoustic and optical phonon scattering, the maximum figure of merit (ZT) of 1L-ZrHfS4 at 1200 K can achieve 1.92 at moderate n-type doping. These findings suggest 1L-ZrHfS4 as a potential material for efficient thermoelectric energy conversion, particularly in applications requiring high temperature operation.

Clathrate structure of YB3C3 for high-performance thermoelectrics with superior mechanical properties

Exploring high-performance thermoelectric materials with improved mechanical properties is important for broadening the application scope and the assembly requirement of stable devices. This work presents an effective strategy to discover hard thermoelectric material by inserting foreign atoms in the rigid covalent framework. We demonstrate this in boron-carbon clathrate VII structure, showing a promising candidate for highly efficient thermoelectric energy conversion, especially with Y atom filled in the cage, with a peak zT of 0.73 at 1,000 K. The ab initio calculations indicate that YB3C3 system has low lattice thermal conductivity of 4.5 W/(m·K) at 1,000 K due to the strong rattling of encaged Y atom. The strongly covalent framework provides highly degenerate band structures consisting of heavy and light electron pockets, which can maintain high carrier mobility arising from small effective mass and thus large group velocity. Consequently, high power factor can be achieved in YB3C3 for both electron and hole doping. In addition, it exhibits well mechanical properties and a Vickers hardness of 23.7 GPa because of the strong covalent boron-carbon framework. This work provides a novel avenue for the search of high-performance thermoelectric materials with excellent mechanical properties, based on boron-carbon clathrate structure.

Effects of vacancy defects on vibrational properties of Ni–Al

The phonon spectra of Ni, Al, and NiAl, as well as their electronic characteristics, are investigated using density functional theory and density functional perturbation theory. Our research on phonon dispersion has concentrated on every high symmetry point of NiAl, both with and without defects. The phonon gap of NiAl is measured to be 1.78 THz between the lowest value of the optical branch and the top bound of the acoustic branch. The NiAl supercell with a center Al vacancy was built to investigate the effects of defects on its vibrational characteristics. The phonon gap of a NiAl crystal at the center of the Brillouin zone with no defect is calculated to be 1.06 THz. This value of the phonon gap is affected by the Al vacancy defect and decreases by 7.67%. The development of phonon spectrum is investigated using electronic structure and properties. The majority of free electrons accumulated at the Fermi level contribute to promoting the vibration. The importance of a heavier element in a compound has also been explored in terms of gap tuning. Reduced thermal conductivity by narrowing the gap between optical and acoustic modes raises the figure of merit (zT) value, which improves the thermoelectric energy conversion efficiency.

Novel Hybrid Modeling and Analysis Method for Steam Reforming Solid Oxide Fuel Cell System Multifault Degradation Fusion Assessment.

Steam reforming solid oxide fuel cell (SOFC) systems are important devices to promote carbon neutralization and clean energy conversion. It is difficult to monitor system working conditions in real time due to the possible fusion fault degradation under high temperatures and the seal environment, so it is necessary to design an effective system multifault degradation assessment strategy for solid oxide fuel cell systems. Therefore, in this paper, a novel hybrid model is developed. The hybrid model is built to look for the system fault reason based on first principles, machine learning (radial basis function neural network), and a multimodal classification algorithm. Then, stack, key balance of plant components (afterburner, heat exchanger, and reformer), thermoelectric performance, and system efficiency are studied during the progress of the system experiment. The results show that the novel hybrid model can track well the system operation trend, and solid oxide fuel cell system working dynamic performance can be obtained. Furthermore, four fault types of solid oxide fuel cell systems are analyzed with thermoelectric parameters and energy conversion efficiency based on transition and fault stages, and two cases are also successful by using the built model to decouple the multifault degradation fusion. In addition, the solid oxide fuel cell multifault degradation fusion assessment method proposed in this paper can also be used in other fuel cell systems.

Decorated dislocations lead to dynamically optimized thermoelectric performance in N-type PbTe

A high thermoelectric energy conversion efficiency requires a large power factor and a low thermal conductivity over a broad temperature range. Optimizing the temperature-dependent carrier concentration and introducing structural defects are effective methods to realize these goals. In this work, we demonstrate that Ag-decorated dislocations can facilitate the dissolution of dopants into the PbTe matrix at elevated temperatures to optimize the carrier concentration in conjunction with the static doping effect of Sb. These spatially aligned and chemically decorated dislocations strongly scatter medium-to low-frequency phonons even at a rather low number density on the order of 1010 cm−2. Moreover, these dislocations show little scattering effect on electrons, maintaining a high carrier mobility. As a consequence, a maximum thermoelectric figure-of-merit, zT, of 1.5 at 750 K and an excellent average zT value of 1.1 between 300 and 800 K are obtained in Sb and dilute Ag2Te co-doped n-type PbTe. This work demonstrates that decorated dislocation networks could optimize the electrical and thermal transport properties of thermoelectrics in a wide temperature window.

Topological thermoelectrics: New opportunities and challenges

Due to the great application potential of the efficient interconversion between heat and electricity, thermoelectric materials have long been the research focal points in condensed matter physics and material science. Moreover, since the discovery of topological properties in solid materials, numerous research studies have recently expanded into the role of the topological state in thermoelectrics. Topological insulators and semimetals/metals are characterized by their exotic electronic band structures and quantum surface states, which can provide a new degree of freedom to manipulate thermoelectric properties. Herein, we present a summary on the advantageous combination of topological properties in thermoelectric materials for enhancing the thermoelectric energy conversion efficiency. We demonstrated this concept through some examples on the applications of novel topological materials as a practical strategy towards high thermoelectric performance. Furthermore, the role of different topological states and the corresponding working mechanism is explained, and the related challenges for further development are also discussed. This review article presents an advanced understanding of topological states in a thermoelectric transport mechanism, providing a new strategy to search for outstanding thermoelectric materials.

Thermoelectric and Structural Properties of Sputtered AZO Thin Films with Varying Al Doping Ratios

Nanomaterials can be game-changers in the arena of sustainable energy production because they may enable highly efficient thermoelectric energy conversion and harvesting. For this purpose, doped thin film oxides have been proven to be promising systems for achieving high thermoelectric performances. In this work, the design, realization, and experimental investigation of the thermoelectric properties exhibited by a set of five Al:ZnO thin films with thicknesses of 300 nm and Al doping levels ranging from 2 to 8 at.% are described. Using a multi-technique approach, the main structural and morphological features of the grown thin films are addressed, as well as the electrical and thermoelectrical transport properties. The results show that the samples exhibited a Seebeck coefficient absolute value in the range of 22–33 μV/K, assuming their maximum doping level was 8 at.%, while the samples’ resistivity was decreased below 2 × 10−3 Ohm·cm with a doping level of 3 at.%. The findings shine light on the perspectives of the applications of the metal ZnO thin film technology for thermoelectrics.

Enhanced Thermoelectric Performance by Resonant Doping and Embedded Magnetic Impurity

The thermoelectric energy-conversion efficiency is significantly enhanced by introducing magnetism. Doping $\mathrm{Cr}$ atoms in a ${\mathrm{Cu}}_{2}{\mathrm{Sn}\mathrm{S}}_{3}(\mathrm{CTS})$ matrix modifies the electron density of state (e-DOS) and causes a special electron-transport mechanism by localized impurity spin moments. The localized spin moments cause a spin-spin exchange interaction with the spin of itinerant electrons of the CTS matrix. This is clearly verified in M-T measurement, which deviated from Curie's law. The figure of merit (zT) of the magnetic nanocomposite was 8 times higher than that of pristine CTS by the synergetic effect of modifying e-DOS near the Fermi level and electron transport by localized spin moments.

Comprehensive Model for the Thermoelectric Properties of Two-Dimensional Carbon Nanotube Networks

Networks of semiconducting single-walled carbon nanotubes (SWCNTs) are interesting thermoelectric materials due to the interplay between CNT and network properties. Here, we present a unified model to explain charge and energy transport in SWCNT networks. We use the steady-state master equation for the random resistor network containing both intra- and intertube resistances, as defined through their one-dimensional density of states that are modulated by static Gaussian disorder. The tube-resistance dependence on the carrier density and disorder is described through the Landauer formalism. Electrical and thermoelectric properties of the network are obtained by solving Kirchhoff's laws through a modified nodal analysis, where we use the Boltzmann-transport formalism to obtain the conductivity, Seebeck coefficient, and electronic contribution to the thermal conductivity. The model provides a consistent description of a wide range of previously published experimental data for temperature and charge-carrier-density-dependent conductivities and Seebeck coefficients, with energetic disorder being the main factor to explain the experimentally observed mobility upswing with carrier concentration. Moreover, we show that, for lower disorder energies, the Lorentz factor obtained from the simulation is in accordance with the Wiedemann-Franz law for degenerate-band semiconductors. At higher disorder, deviations from simple band behavior are found. Suppressed disorder energy and lattice thermal conductivity can be the key to higher thermoelectric figures of merit, zT, in SWCNT networks, possibly approaching or even exceeding zT = 1. The general understanding of transport phenomena will help the selection of chirality, composition, and charge-carrier density of SWCNT networks to improve their efficiency of thermoelectric energy conversion.

The Influence of Thermoelectric Properties of Nanomaterial and Applications

To assess the thermoelectric qualities of low-dimensional materials, a nanomaterial was created. Due to its inherent nanoscale structure, a one-dimensional thermoelectric material is predicted to have superior thermoelectric characteristics and low heat conductivity. High efficiency thermoelectric energy conversion devices can be realised by taking use of these better features. Graphene and hexagonal boron nitride (h-BN), two-dimensional nanomaterials, are thermally efficient. Due to the differences in the crystal lattice and electrical structure between graphene and h-BN, a new material with novel thermal properties is created when the two join to produce a planar C-BN hybrid structure or a van der Waals heterostructure. We concentrate on these new qualities while reviewing the two new materials, as their thermal properties affect their structure, size, and number of layers. To assess the thermoelectric qualities of low-dimensional materials, a micro-instrument was created. Due to its inherent nanoscale structure, a one-dimensional thermoelectric material is predicted to have superior thermoelectric characteristics and low heat conductivity. High efficiency thermoelectric energy conversion devices can be realised by taking use of these better features. In this study, we used micromachining to create microdevices to examine the thermoelectric characteristics of low-dimensional materials. The system comprises of a tiny thermocouple with a freely suspended heating element acting as the sensing element. Manipulation was used to place an array of Bi2Te3 nanowires made using the silicon template approach on the microdevice. To show the device’s ability to assess the thermoelectric properties of nanomaterials, measurements of the Bi2Te3 bundle’s electrical, thermal, and Beck coefficients were made. More information about this source text source text necessary for further translation details. We offer a synthetic method for producing Cu2ZnGeSe4 nanocrystals with a limited size range and a predetermined composition. By hot pressing, these nanocrystals were employed to create nanomaterials that were tightly packed. These nanoparticles’ Cu2ZnGeSe4 thermoelectric characteristics have been demonstrated to be very good. A figure of merit of up to 0.55 at 450 °C has already been achieved through early refinement of the nanocrystal composition. The performance of thermoelectric (TE) materials is currently the subject of intense research. One of the suggestions for enhancing their TE performance is nanostructuring. However, a nanomaterial’s shape can have a big impact on how it behaves under tension. In this study, we showed that this action uses a microwave-assisted chemical pathway to create zinc oxide (ZnO) in two distinct forms. The molar ratios of the initial precursors were altered to create nanoparticles (NPs) and nanorods (NRs). According to the results, NRs have better TE properties than NPs, especially at higher temperatures.

Role of inter-electrode coupling on thermoelectricity in an interferometric geometry: a new proposition

Efficient thermoelectric (TE) energy conversion is one of the most desirable solutions of our current day energy crisis. Exploiting the effect of quantum interference among electronic waves, in this work we propose a prescription of getting high TE efficiency, the so-called figure of merit (ZT), considering an interferometric geometry where a loop conductor is clamped between two heat baths. Unlike conventional junction configurations, we introduce an additional path for electron transfer directly from source to drain, due to their close proximity. The interplay between different paths leads to an enhanced ZT (ZT > 1). Moreover, the efficiency can be further regulated by tuning the inter-electrode coupling. The effects of magnetic flux threaded by the ring and disorder are also discussed. Our proposed prescription may lead to a new route of designing tunable TE devices at nanoscale level.

Waste Heat Driven Microporous-Carbon-Based Thermo-Electrochemical Cells

Solid-state thermoelectrics have focused on thermal to electrical energy conversion for many decades. Nevertheless, the thermoelectric energy conversion efficiency is limited by the intrinsic coupling between material properties such as electrical conductivity and the Seebeck coefficient, which reduces its efficiency despite much progress in this field. Here, we demonstrate a simple, cost-effective platform for harvesting waste heat into electricity via thermo-electrochemical cells (or thermocells) that utilize the effect of temperature on electrochemical redox potentials (i.e., the electrochemical Seebeck effect). In our preliminary experiments, coin cell type thermocells were prepared using microstructured carbon electrodes, aqueous ferricyanide/ferrocyanide redox couple, and commercial polymer separators. The wettability of the electrodes was varied by changing the duration of reactive ion etching (RIE), which improved the power performance. The highest output power (~ 75 nW) was recorded for RIE time of 3 minutes with a load of 1 kΩ. Separately, we also tested thermocells using natural wood-derived cellulose as separator materials. The performance of our thermocells will be presented, and their ability to directly power small electronic devices will be discussed.

Theoretical Understanding of thermoelectric energy conversion efficiency in Lead-Free halide double perovskites showing intrinsic defect tolerance

Thermoelectric devices based on the Seebeck effect can directly convert waste heat to electricity, but the demand for better thermoelectric materials remains unfulfilled. The lead-free halide double perovskites have recently shown promises for their stability and environment-friendly nature, but impacts from intrinsic defects (vacancies and anti-sites) on their thermoelectric performance remains elusive. Combing first-principle calculations, the Boltzmann transport theory, and the defect formation theory, we investigate the thermoelectric properties of lead-free double perovskite Cs2NaInCl6, taking the intrinsic defects into consideration. Our results demonstrate that the pristine Cs2NaInCl6 presents thermodynamic, mechanical, and dynamic stability. The band edges are mainly comprised of the electrons from In and Cl atoms. Furthermore, the double perovskite has an ultra-low lattice thermal conductivity and a high Seebeck coefficient, while showing a small charge carrier relaxation time and electric conductivity. Promisingly, the maximum ZT values can reach as high as ∼ 1.36 and ∼ 1.44 at 800 K temperature, respectively, with optimal extrinsic carrier concentrations of ∼ 1.9 × 1019 and 5.8 × 1020 cm−3 for N- and P-type carriers (holes and electrons), and the maximum power generation efficiency can reach ∼ 14% (for P-type) when the hot-side temperature is 800 K. Among various intrinsic defect types, we determine the preferable defect types in Cs2NaInCl6 based on the minimal defect formation energy criteria. The free carriers can be switched from N- to P-type under these two preferable defects, respectively, with Cl and Na vacancies. Even under a very high defect concentration of 2.1 × 1019/cm3 considered here, the extra carrier concentrations induced by the defects are only ∼ 1017 cm−3 at 800 K, showing strong defect tolerance in carrier concentration. This work suggests that lead-free halide double perovskites are promising thermoelectric materials, and they show strong intrinsic defect tolerance that prevents a negative impact on the extrinsic doping-controlled carrier concentrations.

Dynamic doping and Cottrell atmosphere optimize the thermoelectric performance of n-type PbTe over a broad temperature interval

High thermoelectric energy conversion efficiency requires a large figure-of-merit, zT, over a broad temperature range. To achieve this, we optimize the carrier concentrations of n-type PbTe from room up to hot-end temperatures by co-doping Bi and Ag. Bi is an efficient n-type dopant in PbTe, often leading to excessive carrier concentration at room temperature. As revealed by density functional theory calculations, the formation of Bi and Ag defect complexes is exploited to optimize the room temperature carrier concentration. At elevated temperatures, we demonstrate the dynamic dissolution of Ag2Te precipitates in PbTe in situ by heating in a scanning transmission electron microscope. The release of n-type Ag interstitials with increasing temperature fulfills the requirement of higher carrier concentrations at the hot end. Moreover, as characterized by atom probe tomography, Ag atoms aggregate along parallel dislocation arrays to form Cottrell atmospheres. This results in enhanced phonon scattering and leads to a low lattice thermal conductivity. As a result of the synergy of dynamic doping and phonon scattering at decorated dislocations, an average zT of 1.0 is achieved in n-type Bi/Ag-codoped PbTe between 400 and 825 K. Introducing dopants with temperature-dependent solubility and strong interaction with dislocation cores enables simultaneous optimization of the average power factor and thermal conductivity, providing a new concept to exploit in the field of thermoelectrics.

Extensive Analysis on the Thermoelectric Properties of Aqueous Zn-Doped Nickel Ferrite Nanofluids for Magnetically Tuned Thermoelectric Applications.

Because of the ever-increasing consumption of energy, higher-efficiency thermoelectric materials are in more demand. In this regard, initially, ZnxNi(1-x)Fe2O4 nanoparticles were synthesized using a co-precipitation technique and investigated using Rietveld refinement and Brunauer-Emmett-Teller (BET) analyses. Then, they were dispersed in water to obtain stable 1 vol % of aqueous ZnxNi(1-x)Fe2O4 nanofluids and their viscous, electrical, thermal, and thermoelectric properties were analyzed in the absence and presence of a magnetic field. The Rietveld refinement revealed the formation of single phase spinel ferrite structures and cationic distribution of ZnxNi(1-x)Fe2O4 nanoparticles, whereas BET analysis revealed the surface area of the nanoparticles. The viscosity studies proved the pseudo-plastic shear thinning behavior and dipole-dipole interactions of ZnxNi(1-x)Fe2O4 nanofluids. The electrical conductivity, thermal conductivity, and Seebeck coefficient studies revealed that the maximum enhancement was observed for the Zn0.2Ni0.8Fe2O4 nanofluid, which was attributed to the enhanced electrical double layer formation and Brownian motion of nanoparticles in the nanofluid. The enhancement in the properties of synthesized nanofluids in the presence of a magnetic field was attributed to the formation of chain-like structures, which was substantiated through the magneto-viscosity studies. The thermoelectric energy conversion efficiency of ZnxNi(1-x)Fe2O4 nanofluids was calculated which showed that the maximum enhancement of 27% was observed in the Zn0.2Ni0.8Fe2O4 nanofluid at 770 G. The observed results proved that the synthesized nanofluids are magnetically tunable thermoelectric materials which are suitable for waste heat energy harvesting applications.

Scanning tunneling microscopy of Bi2Te3 films prepared by pulsed laser deposition: from nanocrystalline structures to van der Waals epitaxy

Bi2Te3 is a material with high efficiency of thermoelectric energy conversion. Recently, it was also recognized as a topological insulator, and is often used as the basis for creation of other types of topological matter. Pulsed laser deposition (PLD) is widely considered as a simple method for growing of multicomponent films, but not as a tool for van der Waals epitaxy. We demonstrate here that the van der Waals epitaxy of Bi2Te3 is indeed impossible in vacuum PLD, but is possible in the presence of a background gas, which is confirmed by the results of scanning tunneling microscopy and spectroscopy studies. Results of ab initio calculations reproduce tunneling spectra of the first three terraces of epitaxial films of Bi2Te3. In addition, an unusual hexagonal superstructure resembling a charge-density wave is observed in overheated films.