Prospective Thermoelectric Materials Research Articles

N-Type AlCuFeMn Medium-Entropy Alloy with Reduced Thermal Conductivity: A Prospective Thermoelectric Material

n-Type AlCuFeMn Medium-Entropy Alloy with Reduced Thermal Conductivity: A Prospective Thermoelectric Material

Enhanced thermoelectric properties and thermal stability of Cu1.8S-rGO nanocomposite by low energy carrier filtering effect

Cu1.8S has received a lot of interest as a prospective thermoelectric material with the best performance and abundant resources. While high charge carrier concentration contributes to the high electrical conductivity and power factor values, grain-boundary engineering is required to improve the phonon scattering and thermal stability of Cu1.8S. We used a simple process that combined nanoparticles via mechanical alloying and post-annealing to introduce the reduced graphene oxide (rGO) heterointerface into the Cu1.8S matrix. A significant enhancement of power factor has been realized that the highest power factor is 721 μWm−1 K−2 at 550 K in the composite Cu1.8S/rGO with 10 % rGO, which is higher than the pure Cu1.8S. Furthermore, following four cycles of testing from ambient temperature to 550 K, the composite demonstrated excellent repeatability of power factor, confirming its practical application potential.

CdSe Quantum Dots Enable High Thermoelectric Performance in Solution-Processed Polycrystalline SnSe.

Here, a high peakZTof ≈2.0 is reported in solution-processed polycrystalline Ge and Cd codoped SnSe. Microstructural characterization reveals that CdSe quantum dots are successfully introduced by solution process method. Ultraviolet photoelectron spectroscopy evinces that CdSe quantum dots enhance the density of states in the electronic structure of SnSe, which leads to a large Seebeck coefficient. It is found that Ge and Cd codoping simultaneously optimizes carrier concentration and improves electrical conductivity. The enhanced Seebeck coefficient and optimization of carrier concentration lead to marked increase in power factor. CdSe quantum dots combined with strong lattice strain give rise to strong phonon scattering, leading to an ultralow lattice thermal conductivity. Consequently, high thermoelectric performance is realized in solution-processed polycrystalline SnSe by designing quantum dot structures and introducing lattice strain. This work provides a new route for designing prospective thermoelectric materials by microstructural manipulation in solution chemistry.

Surface and Constriction Engineering of Nanoparticle Based Structures Towards Ultra-Low Thermal Conductivity as Prospective Thermoelectric Materials

ABSTRACT The superior thermal insulating properties of nanostructured semiconductor materials over their bulk counterparts, make them promising candidates for Thermo-Electric (TE) applications. In this study, the superior thermal insulating properties of a new class of one-dimensional nanostructures made by sintering linearly placed nanoparticles, called Nano Particle Chains (NPC) are analyzed for a variety of surface and constriction modifications. The NPC structure which has been shown to be capable of achieving a one-order reduction in thermal conductivity over comparably sized nanowires is revealed to house a new phonon suppression mechanism in addition to commonly discussed phonon boundary scattering and quantum confinement effects. In the current work, this quantum confinement based thermal conductivity reduction mechanism is revealed to be a variation in the phonon Density of States (DoS) along the longitudinal/transport direction of the structure due to the presence of the nanoscale constrictions. Subsequently, the phonons are forced to change the distribution of modes while traveling across the structure, thus resulting in lower thermal conductivity. Additionally, the effects of common phonon suppression techniques such as superlattice, shell alloy, and surface atom removal, used in semiconductor nanostructures are also evaluated on NPC configurations to fully determine the phonon transport characteristics within different classes of the material.

Transport characteristics and lattice dynamics with phonon topology accentuation in layered CuTlX (X: S, Se)

In recent years, numerous Cu-based compounds have attracted a great deal of interest for enhanced thermoelectric energy conversion. Here, we demonstrate that CuTlX (X: S, Se), a layered semiconductor, exhibits low lattice thermal conductivity (κ l ) and a high thermoelectric figure of merit (ZT), using density functional theory calculations and Boltzmann transport theory beyond relaxation time approximation. To evaluate the absolute values of thermoelectric coefficients, different scattering mechanisms such as acoustic deformation potential scattering, impurity phonon scattering, and polar optical phonon scattering are analysed. This low lattice thermal conductivity, which is complemented by a low group velocity and a low phonon lifetime, accounts for the remarkable thermoelectric efficiency in these compounds. In CuTlS, the contribution of the in-plane optical phonon mode to κ l results in a decrease in its value, which might be attributed to the occurrence of Dirac-like crossings with non-trivial topological characteristics, as corroborated by the non-zero Berry curvature value. Overall, the thermoelectric behavior of both compounds is favorable at ambient temperature. Specifically, the out-of-plane direction in CuTlSe presents elevated thermoelectric performance with a high value for the thermoelectric figure of merit, with 1.08 and 1.16 for holes and electrons, respectively, at 300 K at the optimal carrier density of 1019 cm−3 , which well aids in both the electron and phonon transport. We also undertook monolayer examinations of these compounds due to the existence of van der Waals interactions, which predicted strong thermoelectric performance for both carrier concentrations at 300 K. As a result, our study presents a theoretical prediction on transport phenomena that requires experimental verification and should motivate additional research into prospective thermoelectric materials in the same crystal family for device applications.

Enhancement of the thermoelectric properties of Zintl phase SrMg2Bi2 by Na-doping.

Due to their low lattice thermal conductivity and manipulable electronic properties, AB2X2 Zintl phases have been widely studied for thermoelectric applications. This has motivated numerous efforts to focus on the exploration of novel AB2X2 Zintl thermoelectrics. In this study, SrMg2Bi2 was systematically investigated to reveal its potential for thermoelectric application. Pristine SrMg2Bi2 exhibits an intrinsic p-type semiconducting behavior. The Hall carrier concentration (nH) was efficiently increased to ∼9 × 1019 cm-3 by Na-substitution at the Sr site. The increased nH leads to enhanced electrical conductivity, but reduced Seebeck coefficient. Moreover, Na doping effectively decreased the thermal conductivity because of the intensified scattering from defects and lattice distortion. Thus, the zT of the Na-doped SrMg2Bi2 can reach 0.44 and be extremely higher than that of the pristine one. The well-known single parabolic band (SPB) model estimated that the increase in Nv and m* through doping boosts the electrical conductivity. This work sheds light on the discovery of new prospective thermoelectric materials and demonstrates that Bi-based p-type AB2X2 Zintl phases can achieve high thermoelectric performance.

Evaluation of the Thermoelectric Properties and Thermal Conductivity of CH3NH3PbI3-x Cl x Thin Films Prepared by Chemical Routes.

The thermoelectric properties and thermal conductivity of mixed-phase CH3NH3PbI3–xClx thin films have been reported as a function of temperature, ranging from room temperature (RT) to 388 K. Thermoelectric study confirms that CH3NH3PbI3–xClx is a p-type material and the charge carrier transport in CH3NH3PbI3–xClx is governed by polarons and the thermal scattering process. The Peltier function and power factor are found to decrease initially up to ∼325 K, after which they increase with increasing temperature. The position of (EF – EV) of all samples drops down sharply to zero level around 325 K. The avalanches of thermoelectric properties at ∼325 K indicate the existence of tetragonal–cubic phase transition in CH3NH3PbI3–xClx. The calculated thermal conductivity is very low, as desired for thermoelectric materials, due to strong anharmonic interactions. Both the figure of merit (ZT) and device efficiency increase with increasing temperature. However, ZT remains small with temperature. Despite the limitations on the operating temperature range due to phase complexity and small ZT, CH3NH3PbI3–xClx exhibits reasonable thermoelectric power and low thermal conductivity. This signifies the possibility of CH3NH3PbI3–xClx as a prospective thermoelectric material.

Enhanced Thermoelectric Characteristics of Ag2Se Nanoparticle Thin Films by Embedding Silicon Nanowires

A solution-processable Ag2Se nanoparticle thin film (NPTF) is a prospective thermoelectric material for plastic-based thermoelectric generators, but its low electrical conductivity hinders the fabrication of high performance plastic-based thermoelectric generators. In this study, we design Ag2Se NPTFs embedded with silicon nanowires (SiNWs) to improve their thermoelectric characteristics. The Seebeck coefficients are −233 and −240 µV/K, respectively, for a Ag2Se NPTF alone and a Ag2Se NPTF embedded with SiNWs. For the Ag2Se NPTF embedded with SiNWs, the electrical conductivity is improved from 0.15 to 18.5 S/m with the embedment of SiNWs. The thermal conductivities are determined by a lateral thermal conductivity measurement for nanomaterials and the thermal conductivities are 0.62 and 0.84 W/(m·K) for a Ag2Se NPTF alone and a Ag2Se NPTF embedded with SiNWs, respectively. Due to the significant increase in the electrical conductivity and the insignificant increase in its thermal conductivity, the output power of the Ag2Se NPTF embedded with SiNWs is 120 times greater than that of the Ag2Se NPTF alone. Our results demonstrate that the Ag2Se NPTF embedded with SiNWs is a prospective thermoelectric material for high performance plastic-based thermoelectric generators.

Semiconducting chalcogenide Ge-Se-Sb-Cu as new prospective thermoelectric materials

This work examines the electrical and thermoelectric characteristics of Ge25Se65Sb10-xCux (0 ≤ x ≤ 10 at.%) thin films within the temperature range of 300–450 K. In order to get thin films from the bulk specimens, thermal evaporation technique was employed. The electrical conductivity increases from 2.89 × 10−9 Ω−1 m−1 to 6.39 × 10−7 Ω−1 m−1 as the Cu content increases from 0 to 10 at.%. During this investigation, A p-type Ge25Se65Sb10-xCux films were considered, to keep the thermoelectric power positive throughout the temperature range. In addition to that, the dc electrical conductivity and thermoelectric power readings were taken into account to ascertain the level of free carriers presence. As the Cu content increases, the activation energy falls even though power factor; an important thermoelectric parameter, rises. The outcome of the chalcogenide glassy composition investigation revealed that it is a likely source for acquiring high action thermoelectric materials.

Light Element Doping and Introducing Spin Entropy: An Effective Strategy for Enhancement of Thermoelectric Properties in BiCuSeO.

The Seebeck coefficient and carrier mobility in reported doped BiCuSeO system are too small, which limits the improvement of thermoelectric performance. Here, we proposed a novel strategy for optimizing thermoelectric performance by increasing Seebeck coefficient and boosting carrier mobility. We demonstrate that light element Li doping boosts carrier mobility (7.39 cm2 V-1 s-1) due to largely reduced carrier scattering, which results in about 2-fold increase in carrier mobility as compared with reported Bi0.875Ba0.125CuSeO through modulation doping or microstructure texturing. Moreover, the Seebeck coefficient remarkably increases by contribution of spin entropy induced by magnetic ions Mn incorporation. The enhancement of Seebeck coefficient coupled with enhanced electrical conductivity result in high power factor. Furthermore, nanoprecipitates and dual-atom point defect leads to a significant reduction of lattice thermal conductivity. Therefore, a high ZT value of 0.9 was achieved at 873 K through optimizing power factor while maintaining low thermal conductivity. Our findings provide a new perspective for designing prospective thermoelectric materials.

Copper–Nickel and Copper–Cobalt Thermoelectric Generators: Power-Generating Optimization through Structural Geometrics

In this paper of thermoelectric generators, metals are used as the prospective thermoelectric materials or thermoelements on flexible copper (Cu)-clad polyimide substrate. The fabricated thick film generators have planar and lateral structures with lateral heat flow and lateral thermopile layout. Hereby, two prototypes of thermoelectric generators are made, the first employing Cu and nickel (Ni) and the second Cu and cobalt (Co) as their positive and negative thermoelements, respectively. This paper also investigates the roles of geometrical structures such as the thermoleg’s length and width and the generator’s size in promoting elevated thermoelectric power generation. Consequently, the highest performing thermoleg designs (length: 5–20 mm; width: 100– $1000~\mu \text{m}$ ) for the two prototypes are identified as having a length, width, and thickness of 5 mm, $1000~\mu \text{m}$ , and $31~\mu \text{m}$ , respectively, with generator dimensions of 1.1 cm length and 4.3 cm width. Collectively, this design has an accumulated average temperature difference, output power density, and thermoelectric efficiency factor of 60 K, $0.59~\mu $ Wcm−2, and $1.64\times 10^{-\textsf {4}}\,\,\mu $ Wcm−2K−2, respectively, for the Cu–Ni generator, while the corresponding values for the Cu–Co generator are 64 K, $1.15~\mu $ Wcm−2, and $2.81\times 10^{-\textsf {4}}\,\,\mu $ Wcm−2K−2. An improvement factor of 1.71 is realized by the Cu–Co generator compared to the Cu–Ni one due to its larger Seebeck coefficient and figure of merit. This highlights the Cu–Co metallic couple as an encouraging thermoelement in thermoelectricity. Promisingly, the thick film and lateral device structures are more compatible and favorable for metal-based thermoelectric generators.

Enhanced thermoelectric performance of BiCuSeO via dual-doping in both Bi and Cu sites

We investigated the effects of dual-doping in both Bi and Cu sites on the thermoelectric performance of BiCuSeO. The electrical conductivity of Ba and Co dual-doped samples was largely enhanced compared to pristine BiCuSeO due to enhanced carrier concentration. Interestingly, Ba and Co dual-doped samples keep high Seebeck coefficient values as compared to Ba single doped sample, resulting in high power factor. While their thermal conductivities were significantly depressed by enhanced point defect scattering. These favorable factors lead to enhanced ZT of Ba and Co dual-doped samples as compared with Ba single doped sample, Co single doped sample and pristine BiCuSeO. ZT value of 0.082 at 350 K for Ba0.125Bi0.875Cu0.85Co0.15SeO was determined by nearly 32 times higher than that of pristine BiCuSeO. Moreover, this value is about five times higher than that of promising Ba0.125Bi0.875CuSeO. It reveals that dual-doping into both Cu and Bi sites is an effective way for optimizing thermoelectric properties of BiCuSeO. This study opens a new pathway for broadening and designing prospective thermoelectric materials.

Prospects of creating efficient thermoelectric materials based on the achievements of nanotechnology

The elaboration of low-dimensional thermoelectric structures has been shown to allow an increase in the efficiency of thermoelectric materials by the end of the 20th century. The achievements in nanotechnology open up new opportunities in searching for prospective thermoelectric materials and structures. The physical aspects in the creation of low-dimensional thermoelectric structures have been reviewed. The capabilities of developing technologies for the synthesis of thermoelectric structures on the basis of superlattices, quantum wires, and quantum dots have been analyzed. The methods of fabrication and advances in the elaboration of nanocomposite thermoelectric materials have been discussed. The problems in the production of second-generation nanocomposites and their possible solutions have been considered. The methods for diagnosing low-dimensional thermoelectric structures are presented, as well.

Optimization of the spin entropy by incorporating magnetic ion in a misfit-layered calcium cobaltite

Effects of (Lu, Ni) co-doping on spin entropy of Ca3Co4O9+δ have been investigated. Results of this study show that (Lu, Ni) co-doping can be more effective than single Lu doping for optimizing the spin entropy of Ca3Co4O9+δ. X-ray photo-emission spectroscopy confirms a reduction in Co4+ concentration, which leads to enhanced spin entropy from Co sites. The magnetic ions of Ni with unpaired 3d electrons can produce extra spin entropy through a new hopping model, thereby contributing to an increase in total spin entropy. Incorporating magnetic ions is an effective way to optimize the spin entropy of thermoelectric materials. This study opens a new way to broaden and design prospective thermoelectric materials.

ALD Synthesis of PbSe Thin Films inside Porous Si Templates for Innovative Thermoelectric Applications

The IV-VI lead chalcogenides are considered as prospective thermoelectric materials which have their potential applications in green renewable energy by waste heat recovery and infrared devices. Among these materials, PbSe demonstrates a remarkable thermoelectric performance, The thermoelectric figure of merit ZT exceeds 1 for both n-type and p-type PbSe at high temperature. ZT is defined as ZT=σS2T/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity, respectively. In addition, Se element is more abandant and less costly than Te which is a scarce element [1].PbSe thin films on Si substrates have been synthesized by various methods. However, a careful literature search reveals, there are few if any reports on the synthesis of PbSe thin films by atomic layer deposition (ALD). The ALD technique exhibits self-limiting surface reactions in each ALD cycle which consequently results in precise layer thickness control, stoichiometry, composition, uniformity of large area on the substrate. ALD also can be used to deposit conformal film onto very complex substrates or nano-porous template surfaces. This is the one advantageous property of ALD which renders it more competitive and promising in porous template nano-structures. In contrast, magnetron sputtering and PLD cannot be used to coat complex 3D structures with PbSe. Furthermore, the growth temperature of ALD is rather low in comparison with other fabrication processes.In this work we report on the successful synthesis of multiple PbSe thin films on silicon substrates and inside microporous Si templates by thermal ALD, using lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2) and (trimethylsilyl) selenide ((Me3Si)2Se) as the chemical ALD precursors for lead and selenide, respectively. The repetitive structure of nano-porous Si templates offers an additional degree of periodicity in the quest for high ZT thermoelectric films.The XRD and FE-SEM results reveal that the Lead selenide thin films are polycrystalline at deposition temperatures of 170 °C based on Volmer Weber Island growth mode and have characteristic FCC rock-salt crystal structure as shown in Figure (1), (2) and (3).

Chalcogenide Glasses as Prospective Thermoelectric Materials

Despite the fact that glasses have interesting characteristics for thermoelectric (TE) applications, their potential as TE materials has only recently been tested. In a recent article, we focused on glasses based on the Ge20Te80 composition, which has a high Seebeck coefficient, S, showing that in Cux+yGe20−xTe80−y the power factor, S2/ρ (where ρ is the resistivity), strongly improves with increasing Cu concentration. Herein we report on the preparation of glasses in the Cu-Te-As system and their characterization by x-ray diffraction (XRD), differential scanning calorimetry (DSC), and measurements of ρ and S. Our preliminary results show that the melt-spinning technique allows us to extend the Cu-Te-As glassy domain and leads to Tg values that permit use of these glasses in applications up to 100°C. A maximum S2/ρ value of ∼100 μW K−2 m−1 was obtained for the Cu30As15Te55 composition, confirming the potential of these glasses for TE applications.

Applying an electron counting rule to screen prospective thermoelectric alloys: The thermoelectric properties of YCrB 4 and Er 3CrB 7-type phases

An electron counting rule, which was recently expanded to study molecular organometallics, boranes, and metallocenes, is utilized herein to predict the formation of a semiconducting gap or pseudo-gap in the density of states of deltahedral crystalline solids at or near the Fermi energy. It is suggested that this rule may be exploited to screen intermetallic compounds for prospective thermoelectric materials. The rule was applied to several structure types of known deltahedral boride and borocarbide compounds, and its predictions were compared to those of first principles electronic structure calculations when such were available in the literature or to published reports of transport properties. In addition, the rule has been used to predict the properties of several materials for which the electronic structure and properties have not hitherto been reported. In accordance with these predictions, layered ternary boride intermetallic compounds with structure types YCrB 4 and Er 3CrB 7 were synthesized, and the electrical resistivity and Seebeck coefficients of these alloys were measured from room temperature to 1100 K. Alloys of composition RMB 4 (R = Y, Gd, Ho; M = Cr, Mo, W) were found to be n-type semiconductors and to exhibit thermopower up to ∼70–115 μV/K; the band gap was estimated to range from 0.17 to 0.28 eV, depending on composition. Undoped YCrB 4 was measured to have a maximum power factor of 6.0 μW/cm K 2 at 500 K and Fe-doped YMoB 4 of 2.4 μW/cm K 2 near 1000 K.

On the Design of High‐Efficiency Thermoelectric Clathrates through a Systematic Cross‐Substitution of Framework Elements

AbstractType I clathrates have recently been identified as prospective thermoelectric materials for power generation purposes due to their very low lattice thermal conductivity values. The maximum thermoelectric figure of merit of almost all type I clathrates is, however, less than 1 and occurs at, or above, 1000 K, making them unfavorable especially for intermediate temperature applications. In this report, the Zintl–Klemm rule is demonstrated to be valid for Ni, Cu, and Zn transition metal substitution in the framework of type I clathrates and offers many degrees of freedom for material modification, design, and optimization. The cross‐substitution of framework elements introduces ionized impurities and lattice defects into these materials, which optimize the scattering of charge carriers by the substitution‐induced ionized impurities and the scattering of heat‐carrying lattice phonons by point defects, respectively, leading to an enhanced power factor, reduced lattice thermal conductivity, and therefore improved thermoelectric figure of merit. Most importantly, the bandgap of these materials can be tuned between 0.1 and 0.5 eV by adjusting the cross‐substitution ratio of framework elements, making it possible to design clathrates with excellent thermoelectric properties between 500 and 1000 K.

Thermoelectric properties of a clathrate compound Ba8Cu16P30

We report the electrical resistivity (ρ), thermoelectric power (S), thermal conductivity (κ), and specific heat (C) for the clathrate compound Ba8Cu16P30, in which polyhedral cages are composed of Cu and P atoms. Being in contrast to the n-type conduction in most of clathrate compounds, a p-type metallic conduction in this compound is indicated by the positive S, which monotonically increases up to 65 μV/K at 460 K. The analysis of C(T) gives indirect evidence for low-frequency local vibrations of Ba atoms with two Einstein temperatures 120 and 90 K, respectively. These local vibrations lead to a low lattice thermal conductivity of 2.9 W/K m at 300 K. The combination of the metallic resistivity, large thermoelectric power, and low thermal conductivity, makes this compound be a prospective thermoelectric material.