Thermoelectric Figure Of Merit Research Articles

Feature mining for thermoelectric materials based on interpretable machine learning.

In previous laboratory preparation processes, the selection and proportioning of specific experimental parameters often stemmed from the empirical experience of predecessors, necessitating the derivation of the optimal scheme for the target experiment through extensive trial and error. This process typically required the consumption of substantial resources and time. Thanks to the advancement of machine learning technologies, these have gradually become a powerful tool for addressing complex functional problems in material optimization. This study is based on a collected database of thermoelectric materials, aiming to clarify the correspondence between physical characteristics and the thermoelectric figure of merit, zT. The key features that can directly affect the experimental results are identified, and the features that indirectly affect the experimental results are also analyzed. By employing interpretable machine learning methods, this research analyzes critical molecular features in the characterized data, utilizing feature engineering techniques to construct and optimize machine learning models for the selected key features. Furthermore, in the subsequent model fitting and analysis phase, by comparing the efficiency of different feature combinations, the optimal feature descriptors for the current experimental system were determined. The adoption of the aforementioned improved methods endowed the related models with the potential for high-throughput screening, thereby further enhancing the efficiency of experimental optimization.

Influence of Spin-Orbit Coupling on the Optical and Thermoelectric Properties of Lateral MoSe2-WSe2 Heterostructure

In this letter, the spin-orbit coupling (SOC) effect in lateral MoSe2-WSe2 heterostructure was theoretically investigated. The results demonstrate that the SOC effect induces band splitting, narrows the band gap, and reduces the effective mass of electrons. These alterations indicates the enhanced probability of electron transitions from the valence band to the conduction band. Additionally, the SOC effect leads to red shift in the absorption peaks and the presence of SOC effect has transformed the heterostructure from being originally a p-type thermoelectric material to a n-type thermoelectric material, increasing its thermoelectric figure of merit (ZT). Our work not only contributes to a deeper understanding of its physical mechanisms , but also provides a reference for its potential applications in the field of thermoelectric and optical devices.

Synergistic Band and Defect Engineering in ZrNiSn Alloys via Ni-Vacancy Regulation for Realizing High Thermoelectric Performance

Of the n-type half-Heusler material systems, Zr1-xHfxNiSn1-ySby alloys have excellent thermoelectric properties. Typically, the Hf atoms replace Zr site atoms, thus reducing the lattice thermal conductivity. Nonetheless, the excess use of Hf increases the cost of half-Heusler thermoelectric materials, limiting their commercial use. In this study, we used band and defect engineering concurrently to enhance the thermoelectric properties of ZrNiSn-based alloys through the modulation of Ni-structural vacancies. The induction of Ni-structural vacancies not only enhances phonon scattering, decreasing both bipolar and lattice thermal conductivities at high temperatures, but also promotes the formation of multiple electronic valleys close to the Fermi level, enhancing the electrical transport properties. Concurrently, doping ZrNi1-xSn samples with Nb increases the stability of the crystal structure and further refines the thermoelectric parameters. Notably, a thermoelectric figure of merit (ZT) of 1.16 was achieved at 1073 K for Zr0.96Nb0.04Ni0.9Sn, as high as that of Zr1-xHfxNiSn1-ySby samples but without the addition of Hf. This is a novel example of integrating multiple electronic valleys into a ZrNiSn system by introducing Ni-structural vacancies. Crucially, this approach to band structure engineering could be applied to other thermoelectric materials.

Enhanced Carrier Mobility and Thermoelectric Performance by Nanostructure Engineering of PEDOT Thin Films Fabricated via the OCVD Method Using SbCl5 Oxidant

AbstractAir‐stable, lightweight, and electrically conductive conjugated polymers have attracted significant attention for thermoelectric applications, especially in low‐temperature environments. However, their low carrier mobility has limited broader adoption. This study addresses this challenge by investigating the nanostructure of poly(3,4‐ethylenedioxythiophene) (PEDOT) thin films fabricated via oxidative chemical vapor deposition (oCVD) at various deposition temperatures. Through systematic control of the semi‐crystalline orientation and π–π stacking distance, a substantial enhancement in carrier mobility (23.58 ± 1.71 cm2 V−1 s−1) and electrical conductivity (6345 ± 210 S cm−1) is achieved. The thermoelectric power factor demonstrates a direct correlation with deposition temperature, achieving a maximum value of 112.57 ± 4.33 µW m−1 K−2. PEDOT thin films fabricated at higher deposition temperatures show minimal reductions in electrical conductivity as absolute temperature decreased, reflecting a lower resistivity ratio and extended metallic state, as indicated by the metal–insulator transition in the Zabrodskii plot. Incorporating the Seebeck coefficient into the parabolic energy band diagram revealed strong agreement between theoretical and experimental carrier mobility, while also indicating that the energy barrier for intercrystalline charge transport decreases as deposition temperature increases. The highly face‐on orientation and reduced π–π stacking distance in PEDOT thin films facilitate quasi‐1D conduction, thereby enhancing carrier mobility.

An emerging aspirant for solar cell and non-conventional energy applications: Lead free fluoro-perovskites A2TlInF6 (A = K, Rb)

In the present work; structural, electronic, optical, and thermoelectric properties of double perovskites A2TlInF6 (A = K, Rb) have been studied using the ab-initio method in conjunction with full potential Linear Augmented Plane Wave (FP-LAPW) method and PBE-GGA potential. Structural properties, cohesive energy, and formation enthalpy collectively confirmed the stability of the halide perovskites in a cubic structure with Fm3m symmetry. Electronic properties revealed the p-type semiconductor nature of both materials. The indirect band gap values for K2TlInF6 and Rb2TlInF6 were found to be 3.489 eV and 3.591 eV, respectively, with PBE. With PBE + SOC, the values dropped to 3.445 eV and 3.546 eV, respectively. Optical properties such as Dielectric function εω, Refractive Index nω, Extinction Coefficient κω, Optical Conductivity σ(ω), Reflectivity R(ω), Electron Energy Loss Function L(ω), and Absorption Coefficient αω were determined using PBE-GGA potential. BoltzTraP code was used to determine thermoelectric properties, namely, Seebeck Coefficient (S), Electrical Conductivity (σ), Thermal Conductivity (K), Power Factor (PF), and Figure of merit (ZT) which were studied in detail. The study suggests halide-based double perovskites may have the potential for solar energy utilization due to their high absorption coefficient, large values of refractive index, and optimal values of the figure of merit.

A comprehensive analysis of structural, electronic, optical, mechanical, thermodynamic, and thermoelectric properties of direct band gap Sr3BF3 (B = As, Sb) photovoltaic compounds: DFT-GGA and mBJ approach

This study evaluates the physical properties of lead-free Sr3BF3 (B = As, Sb) photovoltaic compounds including structural, electronic, mechanical, optical, thermodynamic, and thermoelectric behavior using calculations based on DFT approach. Born stability criteria and formation enthalpy estimates show that the compounds under study are mechanically and thermodynamically stable. The initial lattice constants for Sr3AsF3 and Sr3SbF3 were determined to be 5.71 Å and 5.97 Å, respectively. While simulating the compounds under pressure, lattice constants, cell volumes, and bond lengths decrease. The band structure investigation shows that these compounds are semiconducting with an adjustable direct bandgap. The electronic band gap contracts by pressure, shifting the material from ultraviolet to the visible spectrum. This modification enhances electron transition from valence band maxima to conduction band minima, enhancing optical efficiency. The shift and rise in ductility and machinability index under pressure ensures good lubrication, low friction, and significant plastic deformation suitable for many industrial applications. Simultaneously, the static dielectric constant increases, increasing absorption and conductivity and red-shifting the optical spectrum, and reducing reflectivity in the visible spectrum. The thermodynamic behavior of the compounds was affected by both pressure and temperature variation. The thermoelectric figure of merit becomes closer to unity with a shorter band gap, indicating increased efficiency. Our findings suggest that Sr3BF3 (B = As, Sb) photovoltaic compounds could be used for the invention of next-generation solar cells and thermoelectric devices.

Carbon monochalcogenides/graphene van der Waals heterostructures for sustainable energy harvesting

We constructed the van der Waals (vdW) heterostructures by stacking graphene (G) on top of carbon-based monochalcogenides (CX; X = S, Se, and Te) monolayer in two different patterns (I and II) and predicted various physical properties through first-principles calculations. Among the six heterostructures, three systems (CS/G in Pattern-I and II, and CSe/G in Pattern-II) were found to be most stable. Additionally, the calculated electronic properties confirmed that the CS/G and CSe/G heterostructures in Pattern II are indirect semiconductors with narrow band gap values of 0.49 and 0.30 eV, respectively. Notably, both heterostructures (CS/G and CSe/G) exhibit significantly larger electron carrier mobilities of 762.83 and 206.84 m2/Vs at room temperature, respectively. Furthermore, intrinsic and interface dipoles in both heterostructures were found to align along the +z axis, enhancing charge transfer at the interface and narrowing the band gap, particularly in CSe/G. This polarization effect contributes to the observed high electron mobility and thermoelectric performance. Electronic transport coefficients like the Seebeck coefficient, electrical conductivity, and thermoelectric power factor are predicted using the Boltzmann transport theory implemented in the BoltzTrap code. The highest power factor 249mW/mK2 was achieved for the CSe/G heterostructure at 300K, demonstrating its ability for good thermoelectric purposes. Besides, the computed optical properties revealed the potential of the CS/G heterostructure as a light absorber with an excellent solar light energy conversion efficiency (η) of 23.57 % for solar cell device applications. Our predictions show that the novel 2D CX/G vdW heterostructures could be promising candidates for designing new solar and heat energy harvesting devices.

Thermoelectric Transport Driven by the Hilbert-Schmidt Distance.

The geometric characteristics of Bloch wavefunctions play crucial roles in the properties of electronic transport. Within the Boltzmann equationframework, wedemonstrate that the thermoelectric performance of materials is significantly influenced by the Hilbert-Schmidt distance of Bloch wavefunctions. The connection between the distribution of quantum distance on the Fermi surface and the electronic transport scattering rate is established in the presence of magnetic and nonmagnetic impurities. The general formulation is applied to isotropic quadratic band-touching semimetals, where one can concentrate on the role of quantum geometric effects other than the Berry curvature. It is verified that the thermoelectric power factor can be succinctly expressed in terms of the maximum quantum distance, dmax. Specifically, when dmax reaches one, the power factor doubles compared to the case with trivial geometry (dmax = 0). These findings highlight the significance of quantum geometry in understanding and improving the performance of thermoelectricdevices.

Thermoelectric power factor optimization in hydrothermally synthesized SnO2 nanoparticles by Cu doping

This paper investigates the effect of copper (Cu) doping on the thermoelectric properties of Tin Oxide (SnO2) nanoparticles. The Cu doped samples were prepared with the help of hydrothermal method using different concentration of Cu atoms. Various characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Hall effect and Seebeck measurements are performed to analyze the structural, morphological, electrical and thermoelectric of grown nanomaterials. Based upon the XRD and Raman measurements, it was concluded that the crystal quality of SnO2 samples degraded with increasing the doping concentration of Cu atoms. SEM images reveal that with the increase of Cu concentration, the porosity of the samples decreases, and the distribution of nanoparticle sizes becomes more uniform. The electrical conductivity of the Cu-doped SnO2 nanoparticles increases with increasing the Cu concentration because Cu atoms are supposed to act as donor defects in SnO2 crystal. However, the Seebeck coefficient decreases, indicating a reduced ability to generate a thermoelectric voltage in response to a temperature gradient. The power factor, initially increases with Cu doping, however, beyond an optimal value, the power factor starts to decrease, indicating a saturation or detrimental effect caused by excessive Cu doping.

2D-Penta-PdPS: Gate-Tunable and Thickness-Dependent Thermoelectric Transport.

Pentagonal two-dimensional (2D) materials are notable for unique properties derived from their Cairo pentagonal tiling topology. This study explores the thermoelectric potential of exfoliated penta-palladium-phosphorus-sulfur (PdPS) atomic layers, an air-stable 2D semiconductor with a puckered pentagonal low-symmetry structure, grown via chemical vapor transport (CVT). Thickness-dependent in-plane electrical conductivity (σ) and thermoelectric power factor (PF) of PdPS are investigated from 20-380 K, showing an increase in σ with thickness (11, 13, and 88-layer). Applying back-gate voltage (Vg) modulates the Fermi energy (EF), and as Vg decreases, the Seebeck coefficient (S) rises, achieving S of -700µVK-1 for 11-layer PdPS at -10V, significantly higher than the -400 µVK-1 for 88-layer PdPS. The PF increased with decreasing thickness, peaking at ≈50µW m-1K-2 for 11-layer PdPS, about twice than that of 88-layer PdPS. The high electron mobility (µe) in PdPS is confined to a narrow temperature range, peaking at 300 cm2Vs-1 at 100 K, marking the transition temperature from ionized impurity scattering to acoustic phonon scattering mechanism, consistent across all layer counts. This work highlights the significant impact of quantum confinement in ultrathin bodies in enhancing thermoelectric performance across a wide temperature range.

Data-driven prediction of higher-order structure in carbon nanotube films for high thermoelectric power factor

We optimized the higher-order structures and semiconducting purity of single-walled carbon nanotubes (SWCNTs) to enhance the thermoelectric power factor PF by combining the thermoelectric random stick network (TE-RSN) method and a genetic algorithm. The PF of the optimized films was increased approximately fivefold for initial random structures. In addition, while the random structures showed the maximum PF when the ratio of semiconducting to metallic SWCNTs R s exceeded 0.98, the optimized structures converged to an R s of approximately 0.9. The optimized structures exhibited an increased local density and the peak of alignment angle distribution, leading to an increase in both the electrical conductivity and the Seebeck coefficient. We interpreted the increase in the Seebeck coefficient using a serial model. The results indicated that the reduction in the number of contacts within the paths and the subsequent increase in temperature difference on semiconducting SWCNTs led to the increase in the Seebeck coefficient.

Enhanced thermoelectric power factor in BiSnTe alloy thin films via post-annealing: a structural and electrical study

Enhanced thermoelectric power factor in BiSnTe alloy thin films via post-annealing: a structural and electrical study

High temperature thermoelectric properties of BaxSr2−xFeCoO6 double perovskites

Abstract In this study, environmentally benign BaxSr2-xFeCoO6 (BSFC) double perovskites are synthesized via solid-state reaction route for high-temperature thermoelectric applications. The crystal structure and morphology of the ceramic samples are analyzed using XRD and SEM, respectively. Rietveld refinement of XRD data confirms a cubic structure with Pm3̅m space-group. High-temperature thermoelectric measurements exhibits that substituting Ba for Sr in Sr2FeCoO6 increases the Seebeck coefficient (S) but at the expense of the electrical conductivity (σ). The highest Seebeck coefficient of 117 μV/K has been observed in Ba0.5Sr1.5FeCoO6 at 910 K. Temperature-dependent electrical conductivity measurements indicates a semiconductor-to-metal like transition in all samples, with BSFC (x = 0.1) achieving the highest conductivity of 4 × 104 S m−1 at ∼623 K. The thermoelectric power factor has been enhanced by over 50% with Ba substitution in Sr2FeCoO6. Electron transport in these double perovskites is found to follow the small polaron hopping conduction mechanism.

Inclusion of 2D nanosheets on ZnSb matrix as a unique approach to improve its thermoelectric performance

Enhancing the thermoelectric performance has been made possible by the strategy of introducing an additional phase to the thermoelectric (TE) material. ZnSb: MoS2 nanocomposites are successfully prepared using the solid-state method and sintering. Structural and morphology analysis confirms the inclusion of MoS2 in the ZnSb matrix. The phonon scattering is greatly improved in nanocomposites with newly designed ZnSb: MoS2 interfaces without impairing electron transport. Homogeneous dispersion of MoS2 nanosheets in the ZnSb matrix modulates the carrier effective mass, which is aided by a considerably greater interfacial barrier. The energy filtering effect leads to a significantly higher Seebeck coefficient with strongly reduced phonon conductivity. The addition of MoS2 nanosheets improves the TE power factor (PF) of ZnSb over the temperature of 300 K–673 K. For the ZnSb: MoS2 nanocomposite with 10 wt% of MoS2 achieves a maximum PF of 419.67 μW/mK2 at 673 K, a value that is much greater than pristine ZnSb. It has been shown that zT can be significantly improved by enhancing power factor values and reducing thermal conductivity. A high value of 0.65 is achieved at 673 K for ZnSb:15 % MoS2, which is higher than that for pristine ZnSb. This study lays the path for enhancing the thermoelectric efficiency of p-type ZnSb using interfacial additive of 2D MoS2 nanosheets.

Enhanced Thermoelectric Performance of SnTe via Introducing Resonant Levels

SnTe has emerged as a non-toxic and environmentally friendly alternative to the high-performance thermoelectric material PbTe, attracting significant interest in sustainable energy applications. In our previous work, we successfully synthesized high-quality SnTe with reduced thermal conductivity under high-pressure conditions. Building on this, in this work, we introduced indium (In) doping to further decrease thermal conductivity under high pressure. By incorporating resonance doping into the SnTe matrix, we aimed to enhance the electrical transport properties while maintaining low thermal conductivity. This approach enhances the Seebeck coefficient to an impressive 153 μVK−1 at 735 K, marking a notable enhancement compared to undoped SnTe. Furthermore, we noted a substantial decrease in total thermal conductivity, dropping from 6.91 to 3.88 Wm−1K−1 at 325 K, primarily due to the reduction in electrical conductivity. The synergistic impact of decreased thermal conductivity and heightened Seebeck coefficient resulted in a notable improvement in the thermoelectric figure of merit (ZT) and average ZT, achieving approximately 0.5 and 0.22 in the doped samples, respectively. These advancements establish Sn1−xInxTe as a promising candidate to replace PbTe in thermoelectric applications, providing a safer and more environmentally sustainable option.

Elastic mechanical thermodynamic and thermoelectric properties of pristine and titanium doped Mg2Si: a density functional theory study

Herein, we report a systematic investigation of the effect of Titanium doping on the structural, elastic, mechanical, thermodynamic, and thermoelectric (TE) dynamics of Mg2Si Compounds using first-principle investigation. The present study has been carried out using the full potential linearized augmented plane wave method as implemented inWien2kcode undermBJexchange potentials. The investigations revealed that Mg2-xTixSi compounds have structural stability with cubic phase (Fm-3msymmetry) and possess degenerate semiconducting nature. The analysis of elastic constants revealed mechanical stability of the investigated compounds following Born criteria. Thermodynamic investigations have been carried out in the temperature range of 100-1500 K at zero pressure and the quantities like heat capacity, Debye temperature, Grüneisen constant, and thermal expansion coefficient have been critically analyzed. Lastly, the TE performance of Mg2-xTixSi compounds has been predicted by estimating the thermopower (S2σ) and TE figure of merit (zT) in the temperature range of 300-1500 K. The predicted value ofzTmaxfor Mg2-xTixSi compound is 0.67 at 800 K forx= 0.25 titanium content, suggesting materials promising application for TE energy harvesting and mechanical devices.

Effects of W alloying on the electronic structure, phase stability, and thermoelectric power factor in epitaxial CrN thin films

CrN-based alloy thin films are of interest as thermoelectric materials for energy harvesting. Ab initio calculations show that dilute alloying of CrN with 3 at. % W substituting Cr induce flat electronic bands and push the Fermi level EF into the conduction band while retaining dispersive Cr 3d bands. These features are conducive for both high electrical conductivity σ and high Seebeck coefficient α and, hence, a high thermoelectric power factor α2σ. To investigate this possibility, epitaxial CrWxNz films were grown on c-sapphire by dc-magnetron sputtering. However, even films with the lowest W content (x = 0.03) in our study contained metallic h-Cr2N, which is not conducive for a high α. Nevertheless, the films exhibit a sizeable power factor of α2σ ∼ 4.7 × 10−4 W m−1 K−2 due to high σ ∼ 700 S cm−1, and a moderate α ∼ − 25 μV/K. Increasing h-Cr2N fractions in the 0.03 < x ≤ 0.19 range monotonically increases σ, but severely diminishes α leading to two orders of magnitude decrease in α2σ. This trend continues with x > 0.19 due to W precipitation. These findings indicate that dilute W additions below its solubility limit in CrN are important for realizing a high thermoelectric power factor in CrWxNz films.

Effect of magnetic entropy in the thermoelectric properties of Fe-doped Fe2VAl full-Heusler alloy

The effect of spin entropy on the transport of heat/charge carriers in the Fe-doped full-Heusler alloy Fe2+xVAl1-x with x = 0–0.1 has been studied through low-temperature magnetic and thermoelectric measurements. Magnetization (M) measurements confirm itinerant-electron weak-ferromagnetic behavior. A systematic increase of the magnetic transition temperature TC (from 40 K to 223 K) and of the saturation magnetization (from 0.13 to 0.41μB/Fe) with increasing Fe doping (from x = 0 to 0.1) is observed. Applying a magnetic field causes significant suppression of the Seebeck coefficient (S) and the entropy term (S/T) with a negative magnetoresistance near TC for all weak-ferromagnetic samples, demonstrating a clear effect of spin fluctuations. Analyzing M(T) and S(T), we rule out sizeable magnon drag contributions. A large spin fluctuations-induced enhancement in the thermoelectric power factor PF of about 18 % is achieved for x = 0.1 near TC when compared to measurements in a magnetic field of 7 T. The actual improvement in PF is even much higher, as the S shows a significant enhancement (about 34 %) compared to the estimated diffusion term of S(T) at TC. The number of point defects also increases with Fe doping, causing a significant reduction of the lattice thermal conductivity. This study demonstrates the role of spin fluctuations in enhancing the thermopower/thermoelectric performance of Fe-doped Fe2VAl and opens a vista for the strategy's applicability for various thermoelectric materials.

Exploration of structural, electrical, and thermoelectric properties of two-dimensional [formula omitted] in three phases through ab initio investigations

In this study, the structural, electrical, and thermoelectric properties for three phases of two-dimensional WTe2 have been investigated using first-principles study and semiclassic Boltzmann theory. The results of the electronic density of states have represented band gaps of 1.026, 1.021, and 1.048 eV for phase 1, phase 2, and phase 3, respectively. Furthermore, the largest value of the Seebeck coefficient at 300 K belonged to phase 2 with a value of 1585.21 μV/K at the chemical potential of 0.45 eV. In addition, the largest value of electrical conductivity per relaxation time was related to phase 1 at 300 K with the value of 3.42 × 1020Ω−1 m−1 s−1 at the chemical potential of -1.94 eV. Moreover, the largest value of the thermoelectric power factor per relaxation time occurred for phase 1 at 700 K with a value of 48.62 × 1016μW m−1 K−2 s−1 at the chemical potential of -1.17 eV.

Improving of thermoelectric figure of merit in Sr0.925Dy0.075TiO3 ceramics

Rare earth doped SrTiO3 is one of the most promising oxide materials meeting the safety and stability requirements for potential applications in thermoelectric converters. This work aims to assess the feasibility of engineering SrTiO3-based materials to improve their thermoelectric performance. A comparative analysis of the thermoelectric properties of Sr0.925Dy0.075TiO3 ceramic samples obtained from preliminarily mechanically activated Sr0.925Dy0.075TiO3 nano-powder by two methods – solid-state reaction synthesis and spark plasma sintering – was carried out. Significant differences in the morphology of the samples lead to significant differences in the temperature dependences of electrical resistivity and the Seebeck coefficient. Ceramics obtained by solid-state reaction synthesis exhibit lower porosity and lower electrical resistivity. The thermoelectric power factor of such ceramics is 2–3 times higher than that of samples obtained by spark plasma sintering. The obtained value of thermoelectric figure of merit ZT = 0.41 at T = 673 K for Sr0.925Dy0.075TiO3 is the highest value among n-type oxide thermoelectric ceramics at a given temperature and maintains a tendency to increase with increasing temperature.