Seebeck Effect Research Articles

Thermodynamic Derivation of the Reciprocal Relation of Thermoelectricity.

The Kelvin relation, relating the Seebeck coefficient and the Peltier coefficient, is a theoretical basis of thermoelectricity. It was first derived by Kelvin using a quasi-thermodynamic approach. However, Kelvin's approach was subjected to much criticism due to the rude neglect of irreversible factors. It was only later that a seemingly plausible proof of the Kelvin relation was given using the Onsager reciprocal relation with full consideration of irreversibility. Despite this, a critical issue remains. It is believed that the Seebeck and Peltier effects are thermodynamically reversible, and therefore, the Kelvin relation should also be independent of irreversibility. Kelvin's quasi-thermodynamic approach, although seemingly irrational, may well have touched on the essence of thermoelectricity. To avoid Kelvin's dilemma, this study conceives the physical scenarios of equilibrium thermodynamics to explore thermoelectricity. Unlike Kelvin's quasi-thermodynamic approach, here, a completely reversible thermodynamic approach is used to establish the reciprocal relations of thermoelectricity, on the basis of which the Kelvin relation is once again derived. Moreover, a direct thermodynamic derivation of the Onsager reciprocal relations for fluxes defined as the time derivative of an extensive state variable is given using the method of equilibrium thermodynamics. The present theory can be extended to other coupled phenomena.

Experimental design using the Taguchi method for the development of conductive textiles used in flexible thermoelectric generators

This paper presents several aspects of the robust experimental design methodology using the Taguchi method to develop electrically conductive textiles. These conductive textiles will be used to make thermoelectric generators based on the Seebeck effect. Since the experimental development involves the use of the magnetron sputtering method with more than three variables, the Taguchi method was selected to observe how different parameters (5 independent variables such as argon flow, power, pressure, deposition surface area and metal type used for solid targets) influence the mean and variance of the process performance defined by the thickness of the metal film deposited (dependent variable). In the experimental design framework, the analysis using the Taguchi method, followed by optimisation, helped select the optimal experiments from the set of possible experiments. This methodology reduced the number of experiments by 21–42% and minimised resource consumption (e.g., metal targets, argon, energy).

Mapping the slow and fast photoresponse of field-effect transistors to terahertz and infrared radiation.

Field-effect transistors are capable of detecting electromagnetic radiation from less than 100 GHz up to very high frequencies reaching well into the infrared spectral range. Here, we report on frequency coverage of up to 30THz, thus reaching the technologically important frequency regime of CO2 lasers, using GaAs/AlGaAs high-electron-mobility transistors. A detailed study of the speed and polarization dependence of the responsivity allows us to identify a cross over of the dominant detection mechanism from ultrafast non-quasistatic rectification at low Terahertz frequencies to slow rectification based on a combination of the Seebeck and bolometric effects at high frequencies, occurring at about the boundary between the Terahertz frequency range and the infrared at 10THz.

Temperature Evolution of Magnon Propagation Length in Tm3Fe5O12 Thin Films: Roles of Magnetic Anisotropy and Gilbert Damping.

The magnon propagation length, ⟨ξ⟩, of a ferro-/ferrimagnet (FM) is one of the key factors that controls the generation and propagation of thermally driven magnonic spin current in FM/heavy metal (HM) bilayer based spincaloritronic devices. For the development of a complete physical picture of thermally driven magnon transport in FM/HM bilayers over a wide temperature range, it is of utmost importance to understand the respective roles of temperature-dependent Gilbert damping (α) and effective magnetic anisotropy (Keff) in controlling the temperature evolution of ⟨ξ⟩. Here, we report a comprehensive investigation of the temperature-dependent longitudinal spin Seebeck effect (LSSE), radio frequency transverse susceptibility, and broad-band ferromagnetic resonance measurements on Tm3Fe5O12 (TmIG)/Pt bilayers grown on different substrates. We observe a significant drop in the LSSE voltage below 200 K independent of TmIG film thickness and substrate choice. This is attributed to the noticeable increases in effective magnetic anisotropy field, HKeff (∝Keff) and α that occur within the same temperature range. From the TmIG thickness dependence of the LSSE voltage, we determined the temperature dependence of ⟨ξ⟩ and highlighted its correlation with the temperature-dependent HKeff and α in TmIG/Pt bilayers, which will be beneficial for the development of rare-earth iron garnet based efficient spincaloritronic nanodevices.

Electric Field Switching of Magnon Spin Current in a Compensated Ferrimagnet.

Manipulation of directional magnon propagation, known as magnon spin current, is essential for developing magnonic devices featuring nonvolatile functionalities and ultralow power consumption. Magnon spin current can usually be modulated by magnetic field or current-induced spin torques. However, these approaches may lead to energy dissipation due to Joule heating. Electric-field switching of magnon spin current without charge current is highly preferred but challenging to realize. By integrating magnonic and piezoelectric materials, the manipulation of the magnon spin current generated by the spin Seebeck effect in the ferrimagnetic insulator Gd3Fe5O12 (GdIG) film on a piezoelectric substrate is demonstrated. Reversible electric-field switching of magnon polarization without applied charge current is observed. Through strain-mediated magnetoelectric coupling, the electric field induces the magnetic compensation transition between two magnetic states of the GdIG, resulting in its magnetization reversal and the simultaneous switching of magnon spin current. This work establishes a prototype material platform that paves the way for developing magnon logic devices characterized by all electric field reading and writing and reveals the underlying physics principles of their functions.

Unidirectionally Structured Magnetic Phase-Change Composite Based on Carbonized Polyimide/Kevlar Nanofiber Complex Aerogel for Boosting Solar-Thermo-Electric Energy Conversion.

To realize highly efficient solar-thermo-electric energy conversion for clean electricity power generation, we have developed a new type of unidirectionally structured magnetic phase-change composite comprising a carbonized polyimide (C-PI)/Kevlar nanofiber (KNF) complex aerogel as a 3D carbon skeleton porous supporting material, CoFe2O4 nanoparticles as a magnetic additive, polyethylene glycol (PEG) as a phase-change material, and polypyrrole as a photothermal absorption coating layer. The as-fabricated C-PI/KNF complex aerogel exhibits a unidirectional microstructure, high porosity, robust skeleton frame, ultralight weight, and high thermal conductance. Featured with such unique structure and characteristics, the complex aerogel can offer an effective heat and electron transfer method to ensure highly efficient solar-thermal conversion and photothermal energy storage of the developed composite. The developed composite exhibits a high latent heat capacity of over 150 J g-1, outstanding shape stability along with a low leakage of 0.2 wt %, good thermal cycling stability, and high photothermal conversion efficiency of 84.8%. Based on the Seebeck effect, a solar thermoelectric generation system (STEGS) was constructed with the hot side coupled with the developed composite and the cold side immersed in air and ice water. Under 2.0 kW m-2 solar irradiation, the developed STEGS in ice water obtained maximum output voltage and current of 259.7 mV and 27.1 mA, respectively, which are significantly higher than those in air. The output power of the developed STEGS in an ice water environment is 50.6% higher than that in air under 4.0 kW m-2 solar irradiation. More importantly, the developed STEGS in ice water continuously generated output voltage and current for about 810 s without solar irradiation thanks to the latent heat release by the PEG component within the developed composite. In addition, the introduction of magnetic CoFe2O4 can accelerate solar-thermal conversion through periodic electron motion by the Néel relaxation or Brownian relaxation. This resulted in an increase in the maximum output voltage and current by 13.7 and 11.5%, respectively, under an alternating magnetic field as a result of the magnetism-accelerated solar-thermo-electric conversion. This study offers an innovative approach for developing PCM-based advanced functional materials for solar energy utilization in clean and sustainable electricity generation.

Seebeck Effect in Molecular Wires Facilitating Long-Range Transport.

The study of molecular wires facilitating long-range charge transport is of fundamental interest for the development of various technologies in (bio)organic and molecular electronics. Defining the nature of long-range charge transport is challenging as electrical characterization does not offer the ability to distinguish a tunneling mechanism from the other. Here, we show that investigation of the Seebeck effect provides the ability. We examine the length dependence of the Seebeck coefficient in electrografted bis-terpyridine Ru(II) complex films. The Seebeck coefficient ranges from 307 to 1027 μV/K, with an increasing rate of 95.7 μV/(K nm) as the film thickness increases to 10 nm. Quantum-chemical calculations unveil that the nearly overlapped molecular-orbital energy level of the Ru complex with the Fermi level accounts for the giant thermopower. Landauer-Büttiker probe simulations indicate that the significant length dependence evinces the Seebeck effect dominated by coherent near-resonant tunneling rather than thermal hopping. This study enhances our comprehension of long-range charge transport, paving the way for efficient electronic and thermoelectric materials.

Strategies on the Optimization of Thermoelectric Systems for Heat Transfer Applications: State of the Art Review

Thermoelectric technology is one of the fast-developing technologies in the present days due to its excellent heat transfer and heat conversion capabalities. This uses the electromotive force produced by the temperature difference at each end of the device to produce electricity and vice versa. There are various applications developed based on this thermoelectric technology which includes thermoelectric coolers, thermoelectric generators, and thermoelectric air conditioners. This paper provides a comprehensive analysis of thermoelectric (TE) technologies, starting with a complete summary of their working principles explaining the effects like Seebeck, Peltier, and Thomson effects, as well as optimization techniques, applications, semi-conductor materials used, and potential future developments.

Flexible Ag2Se Thermoelectric Films Enable the Multifunctional Thermal Perception in Electronic Skins.

Skin is critical for shaping our interactions with the environment. The electronic skin (E-skin) has emerged as a promising interface for medical devices to replicate the functions of damaged skin. However, exploration of thermal perception, which is crucial for physiological sensing, has been limited. In this work, a multifunctional E-skin based on flexible thermoelectric Ag2Se films is proposed, which utilizes the Seebeck effect to replicate the sensory functions of natural skin. The E-skin can enable capabilities including temperature perception, tactile perception, contactless perception, and material recognition by analyzing the thermal conduction behaviors of various materials. To further validate the capabilities of constructed E-skins, a wearable device with multiple sensory channels was fabricated and tested for gesture recognition. This work highlights the potential for using flexible thermoelectric materials in advanced biomedical applications including health monitoring and smart prosthetics.

Magnetothermal transport in the spin- 12 easy-axis antiferromagnetic chain

By an exact analytical approach we study the magnetothermal transport in the spin-12 easy-axis Heisenberg model, in particular the thermal conductivity and spin Seebeck effect as a function of anisotropy, magnetic field, and temperature. We stress a distinction between the common spin Seebeck effect with fixed boundary conditions and the one (intrinsic) with open boundary conditions. In the open boundary spin Seebeck effect we find exceptional features at the critical fields between the low field antiferromagnetic phase, the gapless one, and the ferromagnetic at high fields. We further study the development of these features as a function of easy-axis anisotropy and temperature. We point out the potential of these results to experimental studies in spin chain compounds—candidates for spin current generation in the field of spintronics. Published by the American Physical Society 2024

Chiral phonon activated spin Seebeck effect in chiral materials

Chiral phonon activated spin Seebeck effect in chiral materials

Giant Magnon-Polaron Anomalies in Spin Seebeck Effect in Double Umbrella-Structured Tb_{3}Fe_{5}O_{12} Films.

We report a giant hysteretic spin Seebeck effect (SSE) anomaly with a sign reversal at magnetic fields much stronger than the coercive field in a (001)-oriented Tb_{3}Fe_{5}O_{12} film. The high-field SSE enhancement reaches 4200% at approximately 105K over its weak-field value and presents a nonmonotonic dependence on temperature. The unexpected high-field hysteresis of SSE is found to be associated with a magnetic transition of double-umbrella spin texture in TbIG. Nearly parallel dispersion curves of magnons and acoustic phonons around this neoteric transition are supported by theoretical calculations, leading to a high density of field-tuned magnon polarons and consequently an extraordinarily large SSE. Our study provides insight into the evolution of magnon dispersions of double-umbrella TbIG and could potentially boost the efficiency of magnon-polarons SSE devices.

Thermoelectric response across the semiconductor-semimetal transition in black phosphorus

By precisely tuning the ground state of black phosphorus with pressure from the semiconducting to semimetallic state, we track a systematic evolution of the Seebeck coefficient. Thanks to a manifest correlation between the Seebeck coefficient and resistivity, the Seebeck response in each conduction regime, i.e., intrinsic, saturation, extrinsic, and variable range hopping (VRH) regimes, is identified. In the former two regimes, the Seebeck coefficient behaves in accordance with the present theories, whereas in the latter two regimes available theories do not give a satisfactory account for its response. However, by eliminating the extrinsic sample dependence in the resistivity ρ and Seebeck coefficient S, the Peltier conductivity α=S/ρ allows us to unveil the intrinsic thermoelectric response, revealing vanishing fate for α in the VRH regime. The emerged ionized impurity scattering on entry to the semimetallic state is easily surpassed by electron-electron scattering due to squeezing of screening length accompanied by an increase of carrier density with pressure. Each carrier scattering participates an enhancement of the phonon drag contribution to the Seebeck effect, but creates the phonon drag peak with opposite sign at distinct temperature. In the low-temperature limit, a small number of carriers enhances a prefactor of T-linear Seebeck coefficient as large as what is observed in prototypical semimetals. A crucial but largely ignored role of carrier scattering in determining the magnitude and sign of the Seebeck coefficient is indicated by the observation that a sign reversal of the T-linear prefactor is concomitant with a change in dominant scattering mechanism for carriers. Published by the American Physical Society 2024

An experimental study on the performance of TEGs using uniform flow distribution heat exchanger for low-grade thermal energy recovery

Low-temperature thermal energy (<100 °C) is widely present in energy systems and nature, and its utilization is of great significance for energy conservation and carbon reduction. Thermoelectric generator (TEG), without refrigerant and moving parts, can directly convert low-temperature thermal energy into high-grade electricity through the Seebeck effect. One of the biggest defects of TEG is the low efficiency from thermal to electricity. To improve the efficiency of TEG, a staggered fin was arranged in the main flow area for the heat exchanger. Meanwhile, a header with pin-finned and variable triangle geometry is applied in the inlet and outlet of heat exchange to uniform fluid flow. A TEG experimental system containing the heat exchanger whose header with pin-finned and variable triangle geometry was built to evaluate the output performance at variable load resistance, hot and cold source temperature, flow rate, flow direction, and electrically connected array configurations. Moreover, experimental results were compared with other literature. When the inlet hot and cold source temperatures are 40.8–81.0 °C and 20.0–30.0 °C, the TEG system could generate around 0.6–18.8 W with a flow rate of 5 L/min. The TEG system has relative high output performance and a low flow resistance compared to other literatures, and it is the potential to recover low-grade thermal energy recovery.

Proposal of a Thermoelectric Microgenerator based on Seebeck Effect to Energy Harvesting in Industrial Processes

This paper presents a study of the national electric power, showing the Brazil consumes electricity in a year and how much you could save if thermoelectric modules were used in some industries and new cars and planes to capture and transformation of residual thermal energy into electrical energy. The conclusion appears really attractive economically, given the fact that many processes generate residual thermal energy and also energy cogeneration using thermoelectric modules is totally clean, which prevents the emission of greenhouse gases to the environment.

Permanent-magnet-based transverse thermoelectric generator with high fill factor driven by anomalous Nernst effect

A transverse thermoelectric generator for magnetic-field-free and high-density power generation utilizing the anomalous Nernst effect is constructed and its performance is characterized. By alternately stacking two different permanent magnets with the large coercivity and anomalous Nernst coefficients of opposite sign, transverse thermoelectric voltage and power can be generated in the absence of external magnetic fields and enhanced owing to a thermopile structure without useless electrode layers. In the permanent-magnet-based stack, the magnetic attractive force enables easy construction of the thermopile structure with a high fill factor. In this study, we construct a bulk module consisting of 12 pairs of SmCo5- and Nd2Fe14B-type permanent magnets having positive and negative anomalous Nernst coefficients, respectively, whose fill factor reaches ∼80%, whereas that of conventional thermoelectric modules based on the Seebeck effect is typically 30%–60%. We demonstrate magnetic-field-free anomalous Nernst power generation up to 177 µW at a temperature difference of 75 K around room temperature, which corresponds to the largest anomalous Nernst power density of 65 µW/cm2. The presented module structure concept will provide a design guideline for high-performance transverse thermoelectric power generation.

Excellent spin diode and spin-dependent Seebeck effects in hetero-junctions based on ferromagnetic Cr3M4 (M = Se, Te)

Ferromagnetic (FM) half-metals have been regarded as the most promising candidates for spin injection into semiconductors due to their completely spin-polarized electronic states around the Fermi level. To explore the potential application of Cr3M4 (M = Se, Te) in spintronic devices, which are experimentally synthesized FM bulks as well as half-metallic monolayers with high Curie temperature, we propose to design a Bi2Se3/Cr3Se4 van der Waals hetero-junction and a 2D Cr3S4/Cr3Te4 hetero-junction motivated by the recent report on controlling synthesis of Cr x M y based heterostructures. First-principles calculations combined with non-equilibrium Green’s function uncover the perfect spin filtering and spin diode effect in Bi2Se3/Cr3Se4 van der Waals hetero-junction. More interestingly, the Cr3S4/Cr3Te4 hetero-junction shows an excellent spin-dependent Seebeck effect, in which spin-dependent currents with opposite spin orientation can be driven by a temperature gradient to flow in the opposite transport direction. These effects can be understood from the calculated spin-dependent band structures and transmission spectrum. Our results put forward a promising designing and application of spintronic devices based on Cr3M4 (M = Se, Te) FM materials.

Integration of Thermoelectric generators (TEG) in Solar PVT panels

Photovoltaic-thermal hybrid panels (PVT) simultaneously generate electricity and heat with a greater overall efficiency than photovoltaic (PV) and thermal (ST) panels independently. Hybrid PVT-TEG intends to go a step further by integrating thermoelectric modules (TEG) that, based on the Seebeck effect, produce electricity from a temperature difference, thus allowing an additional production of electricity and thus an increase of energy efficiency. In this paper, the design and construction of an experimental installation, consisting of two solar collectors PVT, one of them with 19 TEG modules integrated is presented. This prototype will allow to observe the increase in the electrical production that can be obtained by introducing TEG in PVT modules and the differences in the behaviour (yields and W/Q ratio) between modules with and without TEG.

Comparative Analysis of Loss Mechanism Localization in a Semi-2D SOEC Single Cell Modell: Non-Equilibrium Thermodynamics versus Monocausal-Based Approach

This study aims to theoretically analyze the local entropy production rate in a SOEC single cell at T = 1123.15 K and p = 1 bar. Local entropy rates signify loss mechanisms, crucial for cell design and optimization. A semi-2D SOEC model based on non-equilibrium thermodynamics is developed, supplemented by monocausal correlations for direct comparison. The model is validated using KeraCell III data and grid independence analysis. Simulations of electric current density, temperature, heat flow, and local entropy production for various SOEC operating modes are presented. Coupled transport mechanisms significance is discussed, highlighting the pronounced impact of the Peltier effect on heat flux and temperature. The importance of the Peltier effect in SOECs compared to SOFCs is emphasised. The effects of the Seebeck effect on the potential distribution are superimposed by the dominant ohmic losses in the electrolyte. The localization of entropy production rates shows for exothermic operation that 66.6% of the total losses are due to the predominantly dominant irreversible ion transport in the electrolyte, while the entanglements in the reaction layers contribute 33% and GDLs less than 1%.

The growth mechanism and properties of Bi2212 thin films on miscut substrates by sol-gel method

A sol-gel methodology is employed to prepare Bi2212 thin films on single crystal LaAlO3 miscut substrates with nominal tilt angles of 0°, 5°, 10°, and 15°. The study focuses on examining the phase purity, crystal structure, surface morphology, microstructure, and properties of these thin films. Experimental results indicate that the growth of Bi2212 thin films on miscut substrates proceeds through the step-flow mode using the sol-gel method. Higher tilt angles lead to an increase in the conventional resistivity of Bi2212 thin films. Tilted Bi2212 thin films exhibit a typical transverse Seebeck effect when comparing the resistivity in different directions. Notably, the Seebeck coefficient difference reaches 12 V/K when the substrate tilt angle is set at 15°. Meanwhile, tilted Bi2212 thin films consistently exhibit outstanding superconducting transition temperature (Tc) while demonstrating lower critical current density (Jc) values. These findings offer valuable insights for the development of Bi2212 high temperature superconducting thin films (HTSFs) in thermoelectric and superconductive devices, serving as a reference point for achieving optimal film characteristics.