Seebeck Coefficient Research Articles

Robust, transparent, self-healable, recyclable all-starch-based gel with thermoelectric capability for wearable sensor

Conventional all-starch-based (ASB) gels are weak and lack ductility. The preparation of a robust ASB gel with multi-functionalities e.g., self-healing, anti-freezing, conductivity, and so forth, is highly desirable but challenging. Herein, a new kind of ASB gel was prepared by gelatinizing starch in urea and choline chloride solution (UC) with the aid of water. Its tensile strength was up to 1.08 MPa with a tensile strain of 313 %, and this value hardly changed after 10 days ageing. A high healing efficiency of 98 % can be achieved after 1 h of healing at room temperature, and the healed tensile strength reaches up to ca. 1.06 MPa, which is almost the highest value for ASB gel. The resultant ASB gel can surfer from bending and twisting at −80 °C. Moreover, ASB gel also exhibits excellent biocompatibility and biodegradability. In addition, UC endowed the ASB gel with ion conductivity, allowing it to be used as a flexible strain sensor to monitor human movement. The ion-conductive ASB gel also exhibited thermoelectric ability with a Seebeck coefficient of 2.5 mV K−1, which can be further improved to 5 mV K−1 with a maximum output voltage of 252 mV by introducing a gradient of ionic concentration.

Tuning conduction properties and clarifying thermoelectric performance of P-type half-Heusler alloys TiNi1−xCoxSn (0 ≤ x ≤ 0.15)

TiNiSn is an N-type thermoelectric material with a high-power factor composed of low toxicity and abundant elements. TiNiSn also shows P-type electrical conduction by hole doping. In this study, we tune the conduction properties of TiNi1−xCoxSn (0 ≤ x ≤ 0.15) with Co substitution at the Ni site. The samples were prepared by the arc melting method, and thermoelectric properties were investigated up to 800 K. The results of the Hall effect and the Seebeck coefficient measurements indicate that the majority of charge carriers changes from electrons to holes at x ≥ 0.03, suggesting that Co acts as an acceptor. We report for the first time that Ti0.994Ni1.00Co0.051Sn1.01 exhibits ZT = 0.12 at 675 K. This work reveals that Ti0.994Ni1.00Co0.051Sn1.01 could be a potential P-type thermoelectric material operating at high temperatures.

N-type and P-type series integrated hydrogel thermoelectric cells for low-grade heat harvesting

Low-grade heat is abundant and ubiquitous, but it is generally discarded due to the lack of cost-effective recovery technologies. Ion thermoelectric cells are an affordable and straightforward approach of converting low-grade heat into usable electricity for sustainable power. Despite their potential, ion thermoelectric cells face challenges such as limited Seebeck coefficient and required series integration. Here, we demonstrate that the N-type and P-type conversion of ion thermoelectric cells can be achieved through the phase transition of temperature-sensitive hydrogel containing the triiodide/iodide redox couple. Through the strong interaction between the hydrophobic region of the hydrogel and triiodide, the hydrophobic side selectively captures triiodide and the hydrophilic side repels triiodide, raising the concentration difference of triiodide and thereby increasing the Seebeck coefficient. Specifically, the Seebeck coefficient of the N-type ion thermoelectric cells is 7.7 mV K−1, and the Seebeck coefficient of P-type ion thermoelectric cells is −6.3 mV K−1 (ΔT = 15 K). By connecting 10 pairs of the N-type and P-type ion thermoelectric cells, we achieve a voltage of 1.8 V and an output power of 85 μW, surpassing the reported triiodide/iodide-based ion thermoelectric cells. Our work proposes a phase transition strategy for the N-P conversion of ion thermoelectric cells, and highlights the prospect of series integrated hydrogel ion thermoelectric cells for low-grade heat harvesting.

Cooperative Nernst effect of multilayer systems: Parallel circuit model study

Transverse thermoelectric power generation has emerged as a topic of immense interest in recent years owing to the orthogonal geometry which enables better scalability and fabrication of devices. Here, we investigate the thickness dependence of longitudinal and transverse responses in film-substrate systems, i.e., the Seebeck coefficient, the Hall coefficient, the Nernst coefficient, and the anomalous Nernst coefficient in a unified and general manner based on the circuit model, which describes the system as the parallel setup. By solving the parallel circuit model, we show that the transverse responses exhibit a significant peak, indicating the importance of a cooperative effect between the film and the substrate, arising from circulating currents that occur in these multilayer systems in the presence of a temperature gradient. Finally, on the basis of realistic material parameters, we predict that the Nernst effect in bismuth thin films on doped silicon substrates is boosted to unprecedented values if the thickness ratio is tuned accordingly, motivating experimental validation. Published by the American Physical Society 2024

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.

Enhancing Thermoelectric Performance of Mg3Sb2 Through Substitutional Doping: Sustainable Energy Solutions via First-Principles Calculations

Mg3Sb2-based materials, part of the Zintl compound family, are known for their low thermal conductivity but face challenges in thermoelectric applications due to their low energy conversion efficiency. This study addressed these limitations through first-principles calculations using the CASTEP module in Materials Studio 8.0, aiming to enhance the thermoelectric performance of Mg3Sb2 via strategic doping. Density functional theory (DFT) calculations were performed to analyze electronic properties, including band structure and density of states (D.O.S.), providing insights into the influence of various dopants. The semiclassical Boltzmann transport theory, implemented in BoltzTrap (version 1.2.5), was used to evaluate key thermoelectric properties such as the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and electronic figure of merit (eZT). The results indicate that doping significantly improved the thermoelectric properties of Mg3Sb2, facilitating a transition from p-type to n-type behavior. Bi doping reduced the band gap from 0.401 eV to 0.144 eV, increasing carrier concentration and mobility, resulting in an electrical conductivity of 1.66 × 106 S/m and an eZT of 0.757. Ge doping increased the Seebeck coefficient to −392.1 μV/K at 300 K and reduced the band gap to 0.09 eV, achieving an electronic ZT of 0.859 with low thermal conductivity (11 W/mK). Si doping enhanced stability and achieved an electrical conductivity of 1.627 × 106 S/m with an electronic thermal conductivity of 11.3 W/mK, improving thermoelectric performance. These findings established the potential of doped Mg3Sb2 as a highly efficient thermoelectric material, paving the way for future research and applications in sustainable energy solutions.

Impact of valley degeneracy on the thermoelectric properties of zig-zag graphene nanoribbons with staggered sublattice potentials and transverse electric fields.

This study investigates the band inversion of flat bands in zig-zag graphene nanoribbons (ZGNRs) using a tight-binding model. The band inversion results from symmetry breaking in the transverse direction, achievable through deposition on specific substrates such as separated silicon carbide or hexagonal boron nitride sheets. Upon band inversion, ZGNRs exhibit electronic structures characterized by valley degeneracy and band gap properties, which can be modulated by transverse electric fields. To explore the impact of this level degeneracy on thermoelectric properties, we employ Green's function techniques to calculate thermoelectric quantities in ZGNR segments with staggered sublattice potentials and transverse electric fields. Two carrier transport scenarios are considered: the chemical potential is positioned above and below the highest occupied molecular orbital. We analyze thermionic-assisted transport (TAT) and direct ballistic transport (DBT). Level degeneracy enhances the electric power factors of ZGNRs by increasing electrical conductance, while the Seebeck coefficient remains robust in the TAT scenario. Conversely, in DBT, the enhancement of the power factor primarily stems from improvements in the Seebeck coefficient at elevated temperatures.

A Novel Photo‐Activated Dopant for n‐Type Organic Thermoelectrics

AbstractEfficient and air‐stable molecular dopants are critical for optimizing the performance of thermoelectric devices. Despite significant advancements in developing p‐dopants for organic semiconductors, the quest for efficient and air‐stable n‐dopants remains challenging. Here, viologen‐tetraarylborate (VT) is introduced as a promising n‐dopant for thermoelectric applications, demonstrating its remarkable photo‐activation efficiency. After just 1 min of light exposure, a maximum power factor of 8.6 µW m−1 K−2, with a conductivity of 0.86 S cm−1 and a Seebeck coefficient of −346 µV K−1, is achieved for the VT doped PNDI2TEG‐2Tz film. Furthermore, VT exhibits excellent air stability, simplifying the device preparation process by allowing films to be prepared in ambient conditions. Additionally, the unique doping mechanism imparts good air stability to the stock solution of VT and the conjugated polymer, ensuring that the storage time of the stock solution does not affect thermoelectric performance. This innovative approach not only highlights the potential of VT as an efficient n‐dopant but also paves the way for developing novel air‐stable dopants and advancing doping methodologies in thermoelectric material research.

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.

Thermoelectric transport in molecular crystals driven by gradients of thermal electronic disorder.

Thermoelectric materials convert a temperature gradient into a voltage. This phenomenon is relatively well understood for inorganic materials but much less so for organic semiconductors (OSs). These materials present a challenge because the strong thermal fluctuations of electronic coupling between the molecules result in partially delocalized charge carriers that cannot be treated with traditional theories for thermoelectricity. Here, we develop a quantum dynamical simulation approach revealing in atomistic detail how the charge carrier wave function moves along a temperature gradient in an organic molecular crystal. We find that the wave function propagates from hot to cold in agreement with the experiment, and we obtain a Seebeck coefficient in good agreement with experimental measurements that are also reported in this work. Detailed analysis reveals that gradients in thermal electronic disorder play an important role in determining the magnitude of the Seebeck coefficient, opening unexplored avenues for the design of OSs with improved Seebeck coefficients.

A Polymer Film with Very High Seebeck Coefficient and Overall Thermoelectric Properties by Secondary Doping, Dedoping Engineering and Ionic Energy Filtering

AbstractThermoelectric (TE) materials are significant for sustainable development because they can be used to harvest waste heat into electricity. Organic TE materials have unique merits including high mechanical flexibility, low cost, and low intrinsic thermal conductivity. But their TE properties particularly the Seebeck coefficient are notably lower than the inorganic counterparts. Here, a poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) film is reported with a very high Seebeck coefficient and figure of merit (zT) at room temperature through secondary doping, dedoping engineering, and ionic energy filtering. The PEDOT:PSS films are successively treated with acid, base, and vitamin C that is a reductant, and then coated with 1‐ethyl‐3‐methylimidazolium dicyanamide (EMIM:DCA) that is an ionic liquid. This can exhibit a record‐high Seebeck coefficient and power factor of 111 µV K−1 and 1285 µW m−1 K−2, respectively, and the corresponding zT value is 1.05. This is the highest zT value for polymers and polymer composites, and it is comparable to that of the best inorganic TE materials.

Free‐Standing, Multifunctional Thermoelectric and Acoustic Absorbing Nanocomposite Foams

AbstractThermoelectric materials are potential energy harvesting technologies that enable direct, clean conversion between thermal and electrical energy. The efficacy of thermoelectric energy conversion is influenced by the electrical conductivity, thermal conductivity, and Seebeck coefficient. Flexibility, manufacturability, and cost‐effectiveness are also important factors. Polymeric nanocomposites offer advantages in these respects. However, the development of conductive‐polymer thermoelectric materials is limited to an in‐plane architecture, which does not resemble common real‐world scenarios. Moreover, existing works have low thermoelectric properties or rely on additives for performance improvement. In this work, a free‐standing thermoelectric nanocomposite foam is fabricated via the integration of thermally activated microspheres. Due to the microstructure, a thermal conductivity as low as 0.03 W m−1 K−1 is achieved, which is lower than reported for aerogels fabricated via freeze‐drying methods. Additionally, the nanocomposite foam can reach a maximum electrical conductivity of 1.13 S cm−1, power factor of 0.12 µW m−1 K−2, and thermoelectric figure of merit of 3.0 × 10−4. The study also evaluated the compressive stiffness and demonstrated the potential for sound absorption. With the unique combination of the thermoelectric, sound absorption, and mechanical behavior, these nanocomposite foams would offer versatile solutions to address the next generation energy harvesting and acoustic absorption applications.

Influence of Subvalent Twin-Rattler for High n-Type Thermoelectric Performance in Bi13S18Br2 Chalcohalide.

Metal chalcohalides, owing to their higher stability over halides and greater tunability of electronic features over chalcogenides, open new avenues for investigating properties of materials. Complex metal chalcohalides can be a good choice for thermoelectric studies for their halide-like low thermal conductivity and chalcogenide-like high electrical conductivity. Here, we have investigated the thermoelectric properties of n-type Bi13S18Br2 and utilized the concept of Fajans' polarization to describe the formation of a dimer and explained how it can help achieve high thermoelectric figure of merit (zT) of ∼1.0 at 748 K. This zT value is so far the highest-reported value for pristine metal chalcohalides. The existence of subunit in Bi13S18Br2 is experimentally verified by synchrotron X-ray pair distribution function (X-PDF) analysis. The complex structure of Bi13S18Br2 having a large unit cell exhibits simultaneous dimer-cation rattler (i.e., "twin-rattler"), which decreases the lattice thermal conductivity drastically. We observed evidence of such low-energy rattling vibrations from DFT-calculated eigen mode visualizations of the phonon dispersion. The subvalent nature of accommodates an extra electron in Bi(6pz) orbital, which helps form a weakly dispersed donor band just below the Fermi energy (EF), leading to a significant reduction in band gap (0.77 eV), which is favorable for high thermoelectric performance. Consequently, we obtained a semiconducting nature of n-type Bi13S18Br2 with moderate electrical conductivity, as well as a high Seebeck coefficient. Our investigation presents the importance of fundamental chemistry in thermoelectrics and demonstrates the influence of subvalent twin-rattler in triggering high thermoelectric performance in metal chalcohalides.

Electronic Band Structure of a Superconducting Nickelate Probed by the Seebeck Coefficient in the Disordered Limit

Superconducting nickelates are a new family of strongly correlated electron materials with a phase diagram closely resembling that of superconducting cuprates. While analogy with the cuprates is natural, very little is known about the metallic state of the nickelates, making these comparisons difficult. We probe the electronic dispersion of thin-film superconducting five-layer (n=5) and metallic three-layer (n=3) nickelates by measuring the Seebeck coefficient S. We find a temperature-independent and negative S/T for both n=5 and n=3 nickelates. These results are in stark contrast to the strongly temperature-dependent S/T measured at similar electron filling in the cuprate La1.36Nd0.4Sr0.24CuO4. The electronic structure calculated from density-functional theory can reproduce the temperature dependence, sign, and amplitude of S/T in the nickelates using Boltzmann transport theory. This demonstrates that the electronic structure obtained from first-principles calculations provides a reliable description of the fermiology of superconducting nickelates and suggests that, despite indications of strong electronic correlations, there are well-defined quasiparticles in the metallic state. Finally, we explain the differences in the Seebeck coefficient between nickelates and cuprates as originating in strong dissimilarities in impurity concentrations. Our study demonstrates that the high elastic scattering limit of the Seebeck coefficient reflects only the underlying band structure of a metal, analogous to the high magnetic field limit of the Hall coefficient. This opens a new avenue for Seebeck measurements to probe the electronic band structures of relatively disordered quantum materials. Published by the American Physical Society 2024

First principles investigation of structural, elastic, thermoelectric, electronic and optical properties XH3 (X=Ac, La) for hydrogen storage

Efficient hydrogen storage is essential for its use as an energy source. Considering the various methods, hydrogen storage in solid materials shows great promise but requires further research. This study employs density functional theory using the Wien2k, with the LSDA method to determine the stability of this storage mode, and LSDA + mBJ to calculate the electronic, optical, and thermoelectric properties of AcH3 and LaH3. The electronic properties reveal that XH3 (X = Ac, La) exhibits a semiconducting nature with indirect energy gaps in both cases. The analysis of hydrogen storage properties determined the gravimetric hydrogen storage capacities for AcH3 and LaH3 to be 1.297 and 2.086 wt%, respectively. Calculations of the elastic constants validated the mechanical stability of these compounds. Thermoelectric characteristics, including electrical and thermal conductivity, Seebeck coefficient, electronic specific heat capacity, and Pauli magnetic susceptibility, have been evaluated, highlighting their p-type characteristics. The figure of merit indicates their potential for thermoelectric devices. Gravimetric ratios suggest significant hydrogen storage capacity, which could contribute to various transportation and energy applications.

Exploration of lead free half-metallic double perovskites Li2Mo(Cl/Br)6 for spintronic device: DFT-calculations

The intrinsic spin of electrons has revolutionized the various aspects in the field of electronics, like data storage and quantum computing. Magnetic, structural, mechanical, transport and thermoelectric aspects of the Li2Mo(Cl/Br)6 double perovskites have been examined using the Wein2k and BoltzTraP code. These compounds having cubic structure with negative enthalpy of formation confirms their thermodynamic stability. The energy versus volume optimization for both ferromagnetic (FM) and antiferromagnetic phases (AFM) indicate AFM state due to greater release of energy in this configuration. Double exchange model p-d hybridization for partial density of states (PDOS) is investigated in band structures and half-metallicity feature is reported. The spin–orbit interaction with hybridization in d states of Mo and integral magnetic moment reveals strong spin polarization. The thermoelectric features (Seebeck coefficient, power factor, and figure of merit, electrical and thermal conductivities) have also been evaluated for utilization of these compounds in spintronics appliances.

High-Pressure Synthesis of Te-Ge Double-Substituted Skutterudite with Enhanced Thermoelectric Properties.

We synthesized Co4Sb11TexGe1-x (x = 0.5-0.8) using high-pressure, high-temperature conditions at ∼2 GPa and ∼900 K. The microstructure, morphology, and components were characterized via X-ray diffraction, scanning electron microscopy, and electron backscatter diffraction (EBSD). EBSD indicated that the average grain size of Co4Sb11Te0.8Ge0.2 was 1 μm. Electrical conductivity, Seebeck coefficient, and thermal conductivity were measured from 300 to 800 K. The minimum lattice thermal conductivity of Co4Sb11Te0.8Ge0.2 was 0.72 W m-1 K-1, 74% lower than that at 300 K. The introduction of Te and Ge effectively enhanced point effects scattering and location scattering, notably decreasing lattice thermal conductivity. Therefore, the maximum zT value of Co4Sb11Te0.8Ge0.2 was 1.13 at 800 K. These results indicate that high pressure combined with multielement substitution optimized the thermoelectric transport properties of skutterudites.

High‐performance thermoelectric calcium cobaltite nanoribbon ceramic via electrospinning and dual spark plasma texturing

AbstractHigh‐performance polycrystalline calcium cobaltite ceramic was synthesized via electrospinning of nanoribbons, followed by dual‐process compaction using spark plasma sintering and edge‐free spark plasma texturing. The combination of nanoribbon electrospinning and this multistage sintering technique was employed for the first time and resulted in exceptionally well‐textured thermoelectric ceramics. The textured ceramic had excellent thermoelectric properties. At 1073 K, the ceramic exhibited an electrical conductivity of 268 S cm−1, a Seebeck coefficient of 247 µV K−1 and a heat conductivity of 3.3 W m−1 K−1. In addition, the power factor and figure‐of‐merit reached enormously high values of 16.3 µW cm−1 K−2 and 0.53, respectively. This represents the highest thermoelectric performance reported to date not only for electrospun, polycrystalline calcium cobaltite fiber ceramics, but also for undoped polycrystalline calcium cobaltite ceramics.

Electric Structure and Thermoelectric Performance in Cs2O Crystal

In this work, first principles DFT calculations has been employed with anharmonic phonon scatter theory and Boltzmann transport method to perform a exhaustive study on the thermoelectric properties as electronic and phonon transport of layered Cs2O crystal. The results indicate that Cs2O crystal represents a flat-and-dispersive type band structure, which returns a high power factor. In the other hand, low lattice thermal conductivity is discovered in Cs2O semiconductor, combined with its high power factor, the Cs2O crystal is considered a promising thermoelectric material. It is demonstrated that p-type Cs2O could be optimized to exhibit outstanding thermoelectric performance with a maximum ZT value of 0.71 at 500K. Explored by density functional theory calculations, the high ZT value is due to its high Seebeck coefficient S, high electrical conductivity , and low lattice thermal conductivity .

Probing the structural, mechanical, electro-magnetic, thermodynamic and thermoelectric properties of inner-transition based RaXO3 (X: Pr and U) cubic perovskites via first principle calculations

Here, we present ab-initio calculations of the structural, mechanical, electronic, magnetic, thermodynamic and thermoelectric properties of two radium-based perovskites by using density functional theory. These compounds are cubic in nature. Computation of tolerance factor, structural optimization by using the equation of state assures the stability of the materials. Further, we have checked the mechanical stability of the materials by computing the different mechanical parameters. The observed data of B/G and Cauchy pressure for the present materials reveals the ductile nature. The spin polarized band structures and density of states illustrate the half-metallic nature of these materials with the band gap of (3.74 and 4.80) eV in spin down channel for RaPrO3 and RaUO3 alloys respectively. The total magnetic moments calculated via GGA and mBJ approximations were found to be integral in nature (1 and 2) μB, for RaPrO3 and RaUO3 alloys respectively which also is an indication of the half-metallic character of these materials. The effect of temperature and pressure on the different thermodynamic properties like the specific heat capacity, thermal expansion and Gruneisen parameter were studied using the quasi-harmonic Debye model. Finally, we have speculated the temperature dependent thermoelectric properties in terms of Seebeck coefficient, electrical conductivity, thermal conductivity and power factor. The summed -up properties suggest the applications of these materials in thermoelectrics, spintronics and thermoelectric generators outlooks.