Thermoelectric Figure Of Merit Research Articles

Achieving thermoelectric properties of ultra-high-performance concrete using carbon nanotubes and fibers

The study investigated the impact of carbon nanotubes (CNTs), carbon fibers (CFs), steel fibers, and varying water-to-binder (W/B) ratios on the thermoelectric and mechanical properties of ultra-high-performance concrete (UHPC). Flowability tests revealed reduced flow with decreased water content and the addition of CNTs or CFs, particularly pronounced at a lower W/B ratio. Thermal gravimetric analysis and Fourier-transform infrared spectroscopy demonstrated differences in peak intensities and shifts in peaks related to the hydration products of the UHPC by the incorporation of the CNTs and CFs. The compressive strength and tensile performance increased with reduced W/B ratios and the inclusion of steel fibers, whereas the CNTs and CFs affected the strength differently based on their dispersion and interaction with other components that influenced porosity. The presence of steel fibers reduces the percolation threshold for CNTs and CFs, indicating a synergistic effect that enhances electron transport connectivity. The thermal conductivity increased with the addition of CNTs, CFs, and steel fibers, enhancing heat transfer within the UHPC. The thermoelectric figure of merit (ZT) values highlighted the combined impact of CNTs, CFs, steel fibers, and W/B ratios on the thermoelectric efficiency of the UHPC, showing significant improvements with the inclusion of steel fibers and the interplay between the CNTs and W/B ratios. Ultimately, upon introducing 1.5 % steel fibers and 0.3 % CNTs, a substantial enhancement in the thermoelectric ZT was observed, surpassing the standard UHPC values by 12 orders of magnitude.

Extraordinary Thermoelectric Properties of Topological Surface States in Quantum-Confined Cd3As2 Thin Films.

Topological insulators and semimetals have been shown to possess intriguing thermoelectric properties promising for energy harvesting and cooling applications. However, thermoelectric transport associated with the Fermi arc topological surface states on topological Dirac semimetals remains less explored. This work systematically examines thermoelectric transport in a series of topological Dirac semimetal Cd3As2 thin films grown by molecular beam epitaxy. Surprisingly, significantly enhanced Seebeck effect and anomalous Nernst effect are found at cryogenic temperatures when the Cd3As2 layer is thin. In particular, a peak Seebeck coefficient of nearly 500µVK-1 and a corresponding thermoelectric power factor over 30mWK-2m-1 are observed at 5K in a 25-nm-thick sample. Combining angle-dependent quantum oscillation analysis, magnetothermoelectric measurement, transport modeling, and first-principles simulation, the contributions from bulk and surface conducting channels are isolated and the unusual thermoelectric properties are attributed to the topological surface states. The analysis showcases the rich thermoelectric transport physics in quantum-confined topological Dirac semimetal thin films and suggests new routes to achieving high thermoelectric performance at cryogenictemperatures.

Wenzhou TE: A First-Principle-Calculated Thermoelectric Materials Database.

Since the implementation of the Materials Genome Project by the Obama administration in the United States, the development of various computational materials' databases has fundamentally expanded the choice of industries such as materials and energy. In the field of thermoelectric materials, the thermoelectric figure of merit (ZT) quantifies the performance of the material. From the viewpoint of calculations for vast materials, the ZT values are not easily obtained due to their computational complexity. Here, we show how to build a database of thermoelectric materials based on first-principle calculations for the electronic and heat transport of materials. Firstly, the initial structures are classified according to the values of bandgap and other basic properties using the clustering algorithm K-means in machine learning, and high-throughput first principle calculations are carried out for narrow-bandgap semiconductors which exhibit a potential thermoelectric application. The present framework of calculations mainly includes a deformation potential module, an electrical transport performance module, a mechanical and a thermodynamic properties module. We have also set up a search webpage for the calculated database of thermoelectric materials, providing search facilities and the ability to view the related physical properties of materials. Our work may inspire the construction of more computational databases of first-principle thermoelectric materials and accelerate research progress in the field of thermoelectrics.

Enhancement of Phase Stability and Thermoelectric Performance of Meta‐Stable AgSbTe2 by Thermal Cycling Process

AbstractThermoelectric materials are crucial components in thermoelectric devices employed for environmentally friendly solid‐state cooling and waste heat recovery, demanding not only high performance but also superior thermal or phase stability. The high‐performance thermoelectric material AgSbTe2 encounters challenges when utilized in thermoelectric modules due to the precipitation of Ag2Te, resulting in both thermally unstable characteristics and diminished performance. In this study, a thermal cycling process is employed to enhance the thermal stability and thermoelectric performance of AgSbTe2. Through thermal cycling, secondary phases of AgSbTe2 are made uniform, and the undesired Ag2Te is substituted with Sb2Te3 using an optimized thermal cycling process. As a result, the thermal stability of AgSbTe2 is enhanced due to its meta‐stable state, with <5% variance in thermoelectric figure of merit (ZT) measurements, and the ZT value is raised from 0.8 to 1.7 at 643 K through the optimized thermal cycling. The findings indicate that thermal cycling is an effective strategy for enhancing the thermal stability and thermoelectric performance of AgSbTe2, presenting a novel approach for achieving uniform secondary phases in materials with phase separation or phase change characteristics.

Optimizing thermoelectric performance of BiSbPbTe thin films through controlled post-annealing: A comprehensive structural and electronic study

This study investigates the structural and electronic properties of BiSbPbTe thin films, focusing on the impact of post-annealing time and temperature. The X-ray diffraction (XRD) analysis reveals a stable rhombohedral phase formation in all samples, with no secondary phases detected within the detection limit. The high crystallinity of the films is confirmed, and post-annealing leads to an increase in peak intensity, indicating enhanced crystalline structure. Surface morphology analysis using scanning electron microscopy (SEM) demonstrates a transition from inhomogeneous features in as-grown films to homogeneous and dense formations in post-annealed films. The grain size increases with post-annealing time, attributed to diffusion, energy minimization, nucleation, growth, and thermal activation processes. The electronic transport properties, including carrier concentration and conductivity, are influenced by post-annealing temperature and duration. A stable carrier concentration is observed for films post-annealed for up to 2 h, while longer durations decrease due to reduced defect vacancies and grain boundaries. The increase in charge carrier mobility, confirmed by SEM results, contributes to enhanced electrical conductivity. The Seebeck coefficient shows an initial enhancement up to 2 h post-annealing, attributed to defect creation and increased grain boundaries. However, further increases in post-annealing duration result in a decrease in the Seebeck coefficient due to enhanced charge carrier mobility and reduced grain boundaries. The thermoelectric power factor (4.4 μW/cm1K2), determined by the square of the Seebeck coefficient and electrical conductivity, reaches its maximum value in the 2-h post-annealed sample, emphasizing the importance of optimizing post-annealing conditions for improved thermoelectric performance.

Defect modification in enhancing thermopower factor of ZnO films without doping

This study was focused on unraveling the close dependence of the structural, morphological, and thermoelectric properties of sputtered ZnO films on base pressure. The ZnO film deposited at an optimized base pressure of 5 × 10−6 torr exhibited the highest thermoelectric power factor of 374.6 μW/mK2, corresponding to an electrical conductivity of 265 S/cm and a Seebeck coefficient of −124 μV/K at 583 K. The obtained results revealed that the positive effect of base pressure on enhancing thermoelectric properties of ZnO films is attributed to point-defect modification, including zinc vacancies, singly-, and doubly-charged oxygen vacancies. Based on these results, we propose that defect engineering is a facile and effective approach for improving the thermoelectric behavior of ZnO films, even without doping by controlling the sputtering conditions.

Electron-Phonon Interaction Mediated Gigantic Enhancement of Thermoelectric Power Factor Induced by Topological Phase Transition.

We propose an effective strategy to significantly enhance the thermoelectric power factor (PF) of a series of 2D semimetals and semiconductors by driving them toward a topological phase transition (TPT). Employing first-principles calculations with an explicit consideration of electron-phonon interactions, we analyze the electronic transport properties of germanene across the TPT by applying hydrogenation and biaxial strain. We reveal that the nontrivial semimetal phase, hydrogenated germanene with 8% biaxial strain, achieves a considerable 4-fold PF enhancement, attributed to the highly asymmetric electronic structure and semimetallic nature of the nontrivial phase. We extend the strategy to another two representative 2D materials (stanene and HgSe) and observe a similar trend, with a marked 7-fold and 5-fold increase in PF, respectively. The wide selection of functional groups, universal applicability of biaxial strain, and broad spectrum of 2D semimetals and semiconductors render our approach highly promising for designing novel 2D materials with superior thermoelectric performance.

DFT combined to Boltzmann transport theory for optoelectronic and thermoelectric properties investigations for Se (4 & 8 (at.%)) doped Li2SnS3

Cubic Li2SnS3 emerges as a noteworthy ionic conductor and a viable electrode material for lithium secondary batteries. Its application extends to solar cell technologies, owing to its commendable optoelectronic properties and high-power conversion efficiency. In this study, we present density functional theory (DFT)-based first principles calculations for Li2SnS3-xSex (x = 0, 4, and 8% (atomic percent (at.%)) utilizing the modified Becke Johnson (mBJ) approximations, proposing a compelling alternative. Our investigation reveals significant optical absorption in the ultraviolet region for Li2SnS3-xSex (x = 0, 4, and 8%), accompanied by modest effective mass and indirect band gaps of 2.18 eV for the pristine material. Conversely, doped materials exhibit direct band gaps, with values of 2.113 eV for 4% and 2.026 eV for 8%. Furthermore, the calculated thermoelectric power factor underscores the potential and efficacy of Li2SnS3-xSex in thermoelectric energy devices. The findings not only highlight the material’s promise for solar applications but also underscore its candidacy as a novel solid-state electrolyte for lithium-ion batteries. This stems from its robust thermal stability and notable lithium-ion conductivity, positioning Li2SnS3 as a compelling candidate for advanced energy storage technologies.

Topological Electronic Transition Contributing to Improved Thermoelectric Performance in p-Type Mg3Sb2- xBix Solid Solutions.

Topological electronic transition is the very promising strategy for achieving high band degeneracy (NV) and for optimizing thermoelectric performance. Herein, this work verifies in p-type Mg3Sb2- xBix that topological electronic transition could be the key mechanism responsible for elevating the NV of valence band edge from 1 to 6, leading to much improved thermoelectric performance. Through comprehensive spectroscopy characterizations and theoretical calculations of electronic structures, the topological electronic transition from trivial semiconductor is unambiguously demonstrated to topological semimetal of Mg3Sb2- xBix with increasing the Bi content, due to the strong spin-orbit coupling of Bi and the band inversion. The distinct evolution of Fermi surface configuration and the multivalley valence band edge with NV of 6 are discovered in the Bi-rich compositions, while a peculiar two-step band inversion is revealed for the first time in the end compound Mg3Bi2. As a result, the optimal p-type Mg3Sb0.5Bi1.5 simultaneously obtains a positive bandgap and high NV of 6, and thus acquires the largest thermoelectric power factor of 3.54 and 6.93 µW cm-1 K-2 at 300 and 575 K, respectively, outperforming the values in other compositions. This work provides important guidance on improving thermoelectric performance of p-type Mg3Sb2- xBix utilizing the topological electronic transition.

Impact of Spin-Entropy on the Thermoelectric Properties of a 2D Magnet.

Heat-to-charge conversion efficiency of thermoelectric materials is closely linked to the entropy per charge carrier. Thus, magnetic materials are promising building blocks for highly efficient energy harvesters as their carrier entropy is boosted by a spin degree of freedom. In this work, we investigate how this spin-entropy impacts heat-to-charge conversion in the A-type antiferromagnet CrSBr. We perform simultaneous measurements of electrical conductance and thermocurrent while changing magnetic order using the temperature and magnetic field as tuning parameters. We find a strong enhancement of the thermoelectric power factor at around the Néel temperature. We further reveal that the power factor at low temperatures can be increased by up to 600% upon applying a magnetic field. Our results demonstrate that the thermoelectric properties of 2D magnets can be optimized by exploiting the sizable impact of spin-entropy and confirm thermoelectric measurements as a sensitive tool to investigate subtle magnetic phase transitions in low-dimensional magnets.

Study of mechanical, thermodynamic, thermoelectric, and optical properties of Cs2SbAuX6 (X = Cl, Br, I) for energy harvesting applications

The inorganic double perovskites (DPs) Cs2SbAuX6 (X = Cl, Br, I) are an emerging applicant for solar cells, optoelectronic, and thermoelectrics to acquire clean energy. Therefore, the present research thoroughly addresses the mechanical, thermodynamic, optical, and thermoelectric characteristics by modified Becke and Johnson potential of Trans and Balaha (TB-mBJ) and BoltzTraP code. The structural stability is narrated from the tolerance factor and thermodynamic stability by formation energy. Born criteria assure the mechanical existence of cubic structures. The Cs2SbAu(Cl/Br)6 is ductile, and Cs2SbAuI6 has brittle behavior with a metallic nature. The band structures analysis reports the narrow band gaps for Cl/Br and the zero band gap for I-based DPs. The optical properties are studied by dielectric constants, absorption bands, refractive index, and other dependent optical parameters. Lastly, thermoelectric characteristics regarding Seebeck coefficient, electrical conductivity, power factor, thermal conductivity, and figure of merit in the temperature range 200–600K are analyzed. ZT's significant value at room temperature makes them potential candidates for thermoelectric generators.

Understanding of isoelectronic alloying induced energy gap variation for a large enhancement of thermoelectric power factor

Understanding of isoelectronic alloying induced energy gap variation for a large enhancement of thermoelectric power factor

High‐Performance Thermoelectric and Electromagnetic Interference Shielding Derived from MXene/Ag2Se Nanowire Composite Film

AbstractA flexible n‐type composite film consisting of MXene/Ag2Se nanowires (MX‐AS), is synthesized herein via a facile wet chemical sintering process. The thermoelectric properties of the composites with various MXene concentrations are systematically explored. The as‐synthesized 2D MXene exhibits homogeneous intercalation and dispersion of the Ag2Se nanowires. A comparative analysis reveals that these composite films outperform the pristine Ag2Se nanowire films fabricated using the same process. Specifically, the MX‐AS composite film containing 1.5 wt.% MXene exhibits a significant (≈1.25 times) improvement in the maximum thermoelectric power factor (PF), exhibiting a value of ≈933.4 µW m−1 K−2 at 400 K. This enhancement can be attributed to the combination of the remarkable intrinsic Seebeck coefficient of the Ag2Se and the high electrical conductivity of the MXene. Moreover, cyclic bending tests demonstrate the exceptional mechanical durability and flexibility of the composite film, with only an ≈7% decrease in the PF after 1000 cycles. In addition, the as‐prepared MX‐AS composite exhibits a high electromagnetic interference (EMI) shielding efficiency.

C3N based heterobilayers: a potential platform to explore optoelectronic and thermoelectric properties

We theoretically investigate the full thermal transport and optoelectronic features of two established van der Waals heterostructures based on the recently synthesized monolayer of C3N using the machinery of the Boltzmann transport equation and GW+BSE calculations. Among the structures, C3N/hBN tends to exhibit a small indirect gap semiconducting nature with an admixture of comparatively higher ‘flat-and-dispersiveness’ and band degeneracy in the conduction band minima. A nearly comparable high thermoelectric power factor is observed for both carrier types at 300 K and 900 K at specific concentrations. The other material, C3N/Graphene however maintains a low Seebeck coefficient with large electrical conductivity which correctly manifests its metallic character. A combination of low atomic mass, higher anharmonicity and longer lifetime of acoustic phonons in C3N/hBN results in an intermediate lattice thermal conductivity (196 W m−1 K−1) at room temperature as compared to its constituent monolayers. Under heavy n-type doping, C3N/hBN hetero-bilayer displays a figure of merit value of 0.13 (and 0.36) at room temperature (and at 900 K). As per the optical signatures are concerned, C3N/hBN reveals two distinct absorption peaks with a high electron–hole quasiparticle interaction energy correction. Besides both the heterostructures display a much better absorption throughout the spectrum as compared to graphene. We expect these findings will motivate future research in designing thermoelectric and optoelectronic materials made of light mass, earth-abundant and non-toxic elements.

Enhancing Electrical Conductivity and Power Factor in Poly‐Glycol‐Bithienylthienothiophene with Oligoethylene Glycol Side Chains Through Tris (pentafluorophenyl) Borane Doping

AbstractDoping of organic semiconductors has served as an effective method to achieve high electrical conductivity and large thermoelectric power factor. This is of importance to the development of flexible/wearable electronics and green energy‐harvesting technologies. The doping impact of the Lewis acid tris (pentafluorophenyl) borane (BCF) on the thermoelectric performance of poly(2‐(4,4′‐bis(2‐methoxyethoxy)‐5′‐methyl‐[2,2′‐bithiophen]‐5‐yl)‐5‐methylthieno[3,2‐b]thiophene (pgBTTT), a thiophene‐based polymer featuring oligoethylene glycol side chains is investigated. Tetrafluorotetracyanoquinodimethane (F4TCNQ), a well‐established dopant, is utilized as a comparison; however, its inability to co‐dissolve with pgBTTT in less polar solvents hinders the attainment of higher doping levels. Consequently, a comparative study is performed on the thermoelectric behavior of pgBTTT doped with BCF and F4TCNQ at a very low doping level. Subsequent investigation is carried out with BCF at higher doping levels. Remarkably, at 50 wt% BCF doping level, the highest power factor of 223 ± 4 µW m−1 K2 is achieved with an electrical conductivity of 2180 ± 360 S cm−1 and a Seebeck coefficient of 32 ± 1.3 µV K−1. This findings not only contribute valuable insights to the dopant interactions with oxygenated side chain polymers but also open up new avenues for high conductivity thermoelectric polymers in flexible electronic applications.

Machine Learning-Based Predictions of Power Factor for Half-Heusler Phases

A support vector regression model for predictions of the thermoelectric power factor of half-Heusler phases was implemented based on elemental features of ions. The training subset was composed of 53 hH phases with 18 valence electrons. The target values were calculated within the density functional theory and Boltzmann equation. The best predictors out of over 2000 combinations regarded for the p-type power factor at room temperature are: electronegativity, the first ionization energy, and the valence electron count of constituent ions. The final results of support vector regression for 70 hH phases are compared with data available in the literature, revealing good ability to determine favorable thermoelectric materials, i.e., VRhGe, TaRhGe, VRuSb, NbRuAs, NbRuBi, LuNiAs, LuNiBi, TaFeBi, YNiAs, YNiBi, TaRuSb and NbFeSb. The results and discussion presented in this work should encourage further fusion of ab initio investigations and machine learning support, in which the elemental features of ions may be a sufficient input for reasonable predictions of intermetallics with promising thermoelectric performance.

Investigation of the Structural, Mechanical, Electronic, Magnetic, and Thermoelectric Properties of Half Heusler Alloys ZrMnX (X = As, Sb, Te): A DFT‐Based Simulation

AbstractThis study investigates the structural, mechanical, electronic, magnetic, and thermoelectric properties of ZrMnX (X = As, Sb, Te) half Heusler alloys using spin‐polarized density functional theory (SPDFT) with WIEN2K code using full potential linearized augmented plane wave(FP‐ LAPW) technique. Results indicate the ferromagnetic phase’s stability over the non‐magnetic phase in all three alloys. Band structures and density of states highlight the half‐metallic nature of ZrMnX. These alloys exhibit mechanical stability, ductility, and directional properties. Magnetic moments align with the Slater–Pauling rule. Thermoelectric properties, including Seebeck coefficient, electrical and thermal conductivity, and thermoelectric figure of merit, are evaluated using semi‐classical Boltzmann theory. The Seebeck coefficient values for ZrMnX (X = As, Sb, Te) are 144.7, 123.3, and −182.6 µV K−1, respectively at 1200 K with corresponding highest figure of merit 1.0, 0.7, and 1.78. These findings suggest the suitability of these alloys for spintronic devices and high‐temperature thermoelectric applications due to their observed spin‐polarized character and high figure of merit.

Electronic transport and the thermoelectric properties of donor-doped SrTiO3

Strontium titanate (SrTiO3) is widely recognised as an environmentally-benign perovskite material with potential for thermoelectric applications. In this work we employ a systematic modelling approach to study the electronic structure and thermoelectric power factor (PF) of pure SrTiO3 and donor-doped Sr(Ti0.875M0.125)O3 (M = Cr, Mo, W, V, Nb, Ta). We find that the carrier concentration required to optimise the PF of SrTiO3 is on the order of 1021 cm−3, in line with experimental studies. Substitution at the Ti (B) site with 12.5 mol% Nb or Ta is predicted to yield the best PF among the six Group V/VI dopants examined, balancing the Seebeck coefficient and electrical conductivity, and doping with the more abundant Nb would likely give the best price/performance ratio. Although W doping can significantly improve the electrical conductivity, this is at the expense of a reduced Seebeck coefficient. The first-row elements V and Cr have a significantly different impact on the electrical properties compared to the other dopants, forming resonant levels or creating hole carriers and leading to poor thermoelectric performance compared to the second- and third-row dopants. However, the reduction in the bandgap due obtained with these dopants may make the materials suitable for other applications such as photovoltaics or photocatalysis. Our modelling reveals the critical carrier concentrations and best B-site dopants for optimising the electrical properties of SrTiO3, and our predictions are supported by good agreement with available experimental data. The work therefore highlights avenues for maximising the thermoelectric properties of this archetypal oxide material.

Tailoring stress relaxation for dopant-free ZnO thin films with high thermoelectric power factor

In this study, the effects of stress relaxation on the thermoelectric properties (carrier concentration n, Hall mobility μH, weighted mobility μW, density-of-state mass md*, Seebeck coefficient S, and thermopower factor PF) of undoped ZnO films were rationalized in terms of native defects (VO-related defects and Zni-related donors) induced through the deposition temperature (TD) during the sputtering process. All investigated ZnO films exhibited compressive stress and tended to become less compressive with increasing TD. The stress relaxation at high TD resulted in improved film crystallization and decreased native defect concentration, thus significantly enhancing md* through the reduction of intrinsic lattice defects, while less carriers were trapped and scattered by defects. Therefore, n and μ increased simultaneously (by 28 times and one order of magnitude, respectively), markedly enhancing the PF of dopant-free ZnO films.

Refractory and thermoelectric properties of stabilized Tricalcium aluminate allotrope: A first-principles calculation approach

Tricalcium aluminate (Ca3Al2O6) is an indispensable component of Portland cement due to its high strength and reactivity. This study investigates the equilibrium lattice structure as well as the electronic and refractory properties of a newly discovered allotrope of Ca3Al2O6 using density functional theory and random phase approximation methods. Using density functional perturbation theory, we investigate the phonon dispersion of the refined structure’s experimental stability. In addition, the lattice thermal conductivity and thermoelectric figure of merit are computed by solving the Boltzmann Transport Equation with the modified Debye Callaway model and the Relaxation time Approximation methods. The computed Figure of merit, determined by the carrier concentration, indicates a substantial enhancement of 40 to 100-fold, leading to a superior figure of merit of 0.25 and 0.6 when appropriately doped. As a result, we anticipate that stable allotropes of Ca3Al2O6 in the Pm3̄m phase will be useful as energy-harvesting, convective cooling and infrared radiation shield-based cement materials in the cement and concrete industries.