Thermoelectric Semiconductor Research Articles

Room-temperature exceptional plasticity in defective Bi2Te3-based bulk thermoelectric crystals.

The recently discovered metal-like room-temperature plasticity in inorganic semiconductors reshapes our knowledge of the physical properties of materials, giving birth to a series of new-concept functional materials. However, current room-temperature plastic inorganic semiconductors are still very rare, and their performance is inferior to that of classic brittle semiconductors. Taking classic bismuth telluride (Bi2Te3)-based thermoelectric semiconductors as an example, we show that antisite defects can lead to high-density, diverse microstructures that substantially affect mechanical properties and thus successfully transform these bulk semiconductors from brittle to plastic, leading to a high figure of merit of up to 1.05 at 300 kelvin compared with other plastic semiconductors, similar to the best brittle semiconductors. We provide an effective strategy to plastify brittle semiconductors to display good plasticity and excellent functionality simultaneously.

Thermoelectric performance of Cu3InSnSe5 and MnSe pseudo-binary solid solution

Cu3InSnSe5 is a newly discovered copper-based diamond-like thermoelectric semiconductor, whose thermoelectric performance can be further enhanced by the MnSe alloying herein. We observed the formation of MnSe2 precipitates that effectively scattered low-frequency phonons, which significantly reduced the lattice thermal conductivity at mid-to-low temperatures. While a high amount of MnSe alloying led to the formation of MnSe2 precipitates which enhanced the phonons scattering, a smaller MnSe content improved the power factor in a certain as well. Ultimately, our research achieved a peak ZT of 1.00 and an average ZT of 0.50 over the 300–773 K temperature range by 10 mol.% MnSe alloyed Cu3InSnSe5 pseudo-binary solid solution, demonstrating the potential of MnSe alloying for optimizing the thermoelectric performance of copper-based diamond-like semiconductor materials.

Full-shell d-orbitals of interstitial Ni and anomalous electrical transport in Ni-based half-Heusler thermoelectric semiconductors

We systematically investigate the anomalous electronic properties and electrical transport induced by full-shell d10-orbitals of the extra interstitial Nii in Ni-based half-Heusler XNi1+xZ semiconductors. The orbitals from the interstitial Nii have the unique d10 configuration, split into high-energy eg4 orbitals and low-energy t2g6 orbitals under the octahedral crystal field. In XIVNi1+xZIV (XIV=Ti, Zr, Hf; ZIV=Sn, Pb), the localized Nii-eg4 states fall within the intrinsic bandgap leading to a reduced bandgap. In XIIINi1+xZV (XIII=Sc, Y; ZV=Sb, Bi), the Nii-eg4 states overlap with the intrinsic valence bands. Additionally, the interstitial Nii perturb the nearest neighbor X atomic coordination, leading to the splitting of degenerate conduction band minimum, which is stronger in XIIINi1+xZV than XIVNi1+xZIV. Trace amounts of interstitial Nii significantly impact the electrical transport properties. The introduction of the extra interstitial Nii reduces the density of states effective mass, the electron group velocity, and the relaxation time, leading to a decrease of the Seebeck coefficient and electrical conductivity at low and medium temperatures. Nevertheless, the introduction of localized Nii-eg4 states within the bandgap as new valence band maximum attenuate the high-temperature bipolar effect at low carrier concentration intervals, thus maintaining a high thermopower at elevated temperatures. Furthermore, the tuning of the Nii-d10 orbitals by solid solution of both XIVNi1+xZIV and XIIINi1+xZV is expected to further optimize the electrical transport.

Strategic Design and Mechanistic Understanding of Vacancy-Filling Heusler Thermoelectric Semiconductors.

Doping narrow-gap semiconductors is a well-established approach for designing efficient thermoelectric materials. Semiconducting half-Heusler (HH) and full-Heusler (FH) compounds have garnered significant interest within the thermoelectric field, yet the number of exceptional candidates remains relatively small. It is recently shown that the vacancy-filling approach is a viable strategy for expanding the Heusler family. Here, a range of near-semiconducting Heuslers, TiFexCuySb, creating a composition continuum that adheres to the Slater-Pauling electron counting rule are theoretically designed and experimentally synthesized. The stochastic and incomplete occupation of vacancy sites within these materials imparts continuously changing electrical conductivities, ranging from a good semiconductor with low carrier concentration in the endpoint TiFe0.67Cu0.33Sb to a heavily doped p-type semiconductor with a stoichiometry of TiFe1.00Cu0.20Sb. The optimal thermoelectric performance is experimentally observed in the intermediate compound TiFe0.80Cu0.28Sb, achieving a peak figure of merit of 0.87 at 923 K. These findings demonstrate that vacancy-filling Heusler compounds offer substantial opportunities for developing advanced thermoelectric materials.

3D Soft Architectures for Stretchable Thermoelectric Wearables with Electrical Self-Healing and Damage Tolerance.

Flexible thermoelectric devices (TEDs) exhibit adaptability to curved surfaces, holding significant potential for small-scale power generation and thermal management. However, they often compromise stretchability, energy conversion, or robustness, thus limiting their applications. Here, the implementation of 3D soft architectures, multifunctional composites, self-healing liquid metal conductors, and rigid semiconductors is introduced to overcome these challenges. These TEDs are extremely stretchable, functioning at strain levels as high as 230%. Their unique design, verified through multiphysics simulations, results in a considerably high power density of 115.4µWcm⁻2 at a low-temperature gradient of 10°C. This is achieved through 3D printing multifunctional elastomers and examining the effects of three distinct thermal insulation infill ratios (0%, 12%, and 100%) on thermoelectric energy conversion and structural integrity. The engineered structure is lighter and effectively maintains the temperature gradient across the thermoelectric semiconductors, thereby resulting in higher output voltage and improved heating and cooling performance. Furthermore, these thermoelectric generators show remarkable damage tolerance, remaining fully functional even after multiple punctures and 2000 stretching cycles at 50% strain. When integrated with a 3D-printed heatsink, they can power wearable sensors, charge batteries, and illuminate LEDs by scavenging body heat at room temperature, demonstrating their application as self-sustainable electronics.

Colloidal synthetic environmental design towards high-density twin boundaries and boosted thermoelectric performance in Cu5FeS4 icosahedrons

High-density twin boundaries can significantly influence materials’ functional and mechanical properties. In thermoelectrics, twin engineering is able to manipulate the carrier and phonon transport in semiconductors, leading to improved dimensionless figure of merit (zT). However, obtaining twin boundaries with tunable density and uniform distribution in thermoelectric semiconductors is rather challenging. Here, by precisely controlling the temperature of sulfur precursor, the particle size of synthesized Cu5FeS4 icosahedrons can be decreased to produce higher-density twin boundaries. Accordingly, the optimized average distance between two adjacent twin boundaries matches the mean free path of phonons but is much larger than that of carriers, thereby efficiently lowering the lattice thermal conductivity without affecting the carrier mobility significantly. In combination with the enhanced power factor caused by increased carrier concentration, a maximal zT of 0.95 is achieved at 773 K in a p-type Cu5FeS4 derivative material, which is one of the highest values among those in Earth-abundant, environmentally-friendly thermoelectric sulfides. This work uncovers the crucial role of high-density twin boundaries in decoupling the carrier and phonon transport for improved thermoelectric performance in Cu5FeS4-based materials.

Principles and Methods for Improving the Thermoelectric Performance of SiC: A Potential High-Temperature Thermoelectric Material.

Thermoelectric materials that can convert thermal energy to electrical energy are stable and long-lasting and do not emit greenhouse gases; these properties render them useful in novel power generation devices that can conserve and utilize lost heat. SiC exhibits good mechanical properties, excellent corrosion resistance, high-temperature stability, non-toxicity, and environmental friendliness. It can withstand elevated temperatures and thermal shock and is well suited for thermoelectric conversions in high-temperature and harsh environments, such as supersonic vehicles and rockets. This paper reviews the potential of SiC as a high-temperature thermoelectric and third-generation wide-bandgap semiconductor material. Recent research on SiC thermoelectric materials is reviewed, and the principles and methods for optimizing the thermoelectric properties of SiC are discussed. Thus, this paper may contribute to increasing the application potential of SiC for thermoelectric energy conversion at high temperatures.

Study on the possibility of band gap widening of thermoelectric semiconductor α-SrSi2 by isoelectronic elements incorporation

The material α-SrSi2 has considerable application potential as a near room temperature thermoelectric material. However, it has a very narrow band gap which can vanish due to impurities, defects, and grain boundaries. To obtain guidelines for controlling the band gap and improving the thermoelectric properties, we have studied the substitution of isoelectronic impurities (Mg, Ca, and Ba for Sr, and C, Ge, and Sn for Si) through first-principles calculations using the Gaussian-Perdew-Burke-Ernzerhof hybrid functional. From these calculations, it was found that:(1) The band gap change due to Ca, Ba, Ge, and Sn substitutions is almost the same as that predicted from the change in the lattice constant of pure α-SrSi2.(2) Substitution with C was energetically unfavorable and therefore high levels of substitution would be difficult to achieve. However, it was expected to increase the band gap, contrary to the prediction from the decrease in the lattice constant.(3) An increase in the Mg substitution of the Sr site from 0 at. % to 8 at. % caused a decrease in the lattice constant from 0 % to −1.189 %

Stretchable Thermoelectric Generators for Self‐Powered Wearable Health Monitoring

AbstractAs continuous wearable physiological monitoring systems become more ubiquitous in healthcare, there is an increasing need for power sources that can sustainably power wireless sensors and electronics for long durations. Wearable energy harvesting with thermoelectric generators (TEGs), in which body heat is converted to electrical energy, presents a promising way to prolong wireless operation and address battery life concerns. In this work, high performance TEGs are introduced that combine 3D printed elastomers with liquid metal epoxy polymer composites and thermoelectric semiconductors to achieve elastic compliance and mechanical compatibility with the body. The thermoelectric properties are characterized in both energy harvesting (Seebeck) and active heating/cooling (Peltier) modes, and examine the performance of wearable energy harvesting under various conditions such as sitting, walking, and running. When worn on a user's forearm while walking outside, the TEG arrays are able to power circuitry to collect photoplethysmography (PPG) waveform data with a photonic sensor and wirelessly transmit the data to an external PC using an on‐board Bluetooth Low Energy (BLE) radio. This represents a significant step forward on the path to sustainable body‐worn smart electronics.

Numerical Diagnostics of Solution Blow-Up in a Thermoelectric Semiconductor Model

Numerical Diagnostics of Solution Blow-Up in a Thermoelectric Semiconductor Model

High performance magnesium-based plastic semiconductors for flexible thermoelectrics

Low-cost thermoelectric materials with simultaneous high performance and superior plasticity at room temperature are urgently demanded due to the lack of ever-lasting power supply for flexible electronics. However, the inherent brittleness in conventional thermoelectric semiconductors and the inferior thermoelectric performance in plastic organics/inorganics severely limit such applications. Here, we report low-cost inorganic polycrystalline Mg3Sb0.5Bi1.498Te0.002, which demonstrates a remarkable combination of large strain (~ 43%) and high figure of merit zT (~ 0.72) at room temperature, surpassing both brittle Bi2(Te,Se)3 (strain ≤ 5%) and plastic Ag2(Te,Se,S) and organics (zT ≤ 0.4). By revealing the inherent high plasticity in Mg3Sb2 and Mg3Bi2, capable of sustaining over 30% compressive strain in polycrystalline form, and the remarkable deformability of single-crystalline Mg3Bi2 under bending, cutting, and twisting, we optimize the Bi contents in Mg3Sb2-xBix (x = 0 to 1) to simultaneously boost its room-temperature thermoelectric performance and plasticity. The exceptional plasticity of Mg3Sb2-xBix is further revealed to be brought by the presence of a dense dislocation network and the persistent Mg-Sb/Bi bonds during slipping. Leveraging its high plasticity and strength, polycrystalline Mg3Sb2-xBix can be easily processed into micro-scale dimensions. As a result, we successfully fabricate both in-plane and out-of-plane flexible Mg3Sb2-xBix thermoelectric modules, demonstrating promising power density. The inherent remarkable plasticity and high thermoelectric performance of Mg3Sb2-xBix hold the potential for significant advancements in flexible electronics and also inspire further exploration of plastic inorganic semiconductors.

An automatic apparatus with sliding probe to determine the interface resistivity for thermoelectric semiconductor

Interface resistivity is one pivotal parameter that needs to be minimized in the development of thermoelectric semiconductor device for high energy efficiency. Herein an automatic apparatus to determine the interface resistivity has been established with one digital source meter and three mechatronic linear modules, and operated under the programmed LabVIEW control software. The apparatus is characteristic of the scanning probe that moves on the specimen either in the slide-mode or in the step-mode to record voltage. The sliding velocity and sampling frequency of the probe as well as the boundary materials for holding the specimen are optimized by the linearity of resistance versus displacement and the repeatability in multiple tests. The precision and resolution of the apparatus are verified, and the heterojunction specimens of Bi2Te3 or PbTe with copper are measured. The slide-mode method is compared with the step-mode in terms of the testing time and precision, and the possible error from the Peltier effect and Seebeck voltage is discussed.

Investigation of group 13 elements as potential candidates for p-type dopants in the narrow-gap thermoelectric semiconductor α-SrSi2

AbstractTo investigate the possibility of p-type doping of α-SrSi2, a promising as an eco-friendly thermoelectric material, the energy changes of substitutions of the Si site of α-SrSi2 by group 13 elements were evaluated using first-principles calculations. It is found that Ga doping was the most energetically favorable dopant while In is the most unfavorable. We examined the synthesis of Ga- and In-doped α-SrSi2 using the vertical Bridgeman method and investigated their thermoelectric properties. The Ga atoms were doped to α-SrSi2 successfully up to 1.0 at. %, while In atoms could not be doped as suggested by calculations. For experimental prepared Ga-doped samples, the carrier density was observed to increase with Ga doping, from 3.58 × 1019 cm−3 for undoped α-SrSi2 to 4.49 × 1020 cm−3 for a 1.0 at. % Ga-doped sample at 300 K. The temperature dependence of carrier concentrations was observed to change from negative to positive with increasing Ga content. In addition, the temperature dependence of the Seebeck coefficient was also observed to change from negative to positive with increasing Ga content. The results indicate that α-SrSi2 undergoes a semiconductor–metal transition with Ga doping. The power factor for the undoped sample was quite high, at 2.5 mW/mK2, while the sample with 0.3 at. % Ga had a value of 1.1 mW/mK2 at room temperature.

Deformation and Failure Mechanisms of Element-Substituted Thermoelectric Type-I and Type-VIII Clathrates.

Clathrates are potential "phonon-glass, electron-crystal" thermoelectric semiconductors, whose structure of polyhedron stacks is very attractive. However, their mechanical properties have not yet met the requirements of industrial applications. Here, we report the ideal strength of element-substituted type-I and type-VIII clathrates and the shear deformation mechanism by using density functional theory. The results show that the framework element is the determinant of the intrinsic mechanical properties of the clathrates and is affected by sequential weakening of Si-Ge-Sn. The highest ideal shear strength is 8.71 GPa for I-Ba8Au6Si40 along the (110)/[001] slip system, which is attributed to the formation of higher-energy Si-Si covalent bonds. Meanwhile, the ideal shear strength of Ba-filled I/VIII clathrates (4.51/2.65 GPa) is higher than that of Sr-filled clathrates (3.64 GPa/1.91 GPa). In addition, the strength and ultimate strain of VIII-Ba8Ga16Sn30 can be significantly increased by the structural coordination accommodating with the stiffness of the Ga-Ge bond to achieve simultaneous bond breaking. Our findings demonstrate that the element substitution strategy is an effective approach for designing highly robust clathrates.

Exploiting synergies for high thermoelectric performance in higher manganese silicide-based semiconductors through element Co-doping, energy filtering, and phonon scattering

Higher manganese silicide (HMS) is a promising thermoelectric (TE) semiconductor that operates effectively at medium temperatures. It is characterized by its abundance, environmental friendliness, and desirable impact resistance properties. To enhance the TE properties of HMS, this study employs isoelectronic anion and cation codoping, combined with embedded quantum dot (QD) techniques. The introduction of element doping and nanoinclusions, such as Mn0.96Re0.04(Si0.96Ge0.04)1.79+1.5%Ag2Pt QDs sample, leads to an approximately 85% increase in electrical conductivity. This boost is attributed to the adjustment of the band structure through Re, Ge, and Ag element doping and the charge transfer facilitated by MnSi, Si, and Pt precipitates. Furthermore, the enhanced PF of 1.85 × 10−3 W m−1 K−2 at 773 K is approximately 29% higher than that of pure HMS. Simultaneously, the increase in point defects hampers the improvement of lattice thermal conductivity (κl) by intensively scattering short-wave phonons. This effect is complemented by the precipitation of Si, MnSi, Ag, and Pt nanoparticles, which increases the density of grain boundaries, enhances medium-wave phonon scattering, and substantially reduces κl to 1.45 W m–l K−1 (at 773 K), ∼30% lower than that of pure HMS. The figure of merit of the sample containing 1.5%Ag2Pt QDs at 823 K attains a value of 0.69, which is ∼52% and ∼19% higher than that of pure HMS and Re-Ge-double-doped samples, respectively. The incorporation of isoelectronic codoping, along with the integration of metastable QDs, is demonstrated as an effective strategy for enhancing TE properties.

A nanotwin-based physical model for designing robust layered bismuth telluride thermoelectric semiconductor

A nanotwin-based physical model for designing robust layered bismuth telluride thermoelectric semiconductor

Reversible Thermoelectric Regulation of Electromagnetic and Chemical Enhancement for Rapid SERS Detection.

Actively controlling surface-enhanced Raman scattering (SERS) performance plays a vital role in highly sensitive detection or in situ monitoring. Nevertheless, it is still challenging to achieve further modulation of electromagnetic enhancement and chemical enhancement simultaneously in SERS detection. In this study, a silver nanocavity structure with graphene as a spacer layer is coupled with thermoelectric semiconductor P-type gallium nitride (GaN) to form an electric-field-induced SERS (E-SERS) for dual enhancement. After applying the electric field, the intensity of SERS signals is further enhanced by over 10 times. The thermoelectric field enables fast and reproducible doping of graphene, thereby modulating its Fermi level over a wide range. The thermoelectric field also regulates the position of the plasmon resonance peak of the silver nanocavity structure, rendering synchronous dual electromagnetic and chemical regulation. Additionally, the method enables the trace detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A detailed theoretical analysis is performed based on the experimental results and finite-element calculations, paving the way for the fabrication of high-efficient E-SERS substrates.

Optimization of Mechanical and Thermoelectric Properties of SnTe-Based Semiconductors by Mn Alloying Modulated Precipitation Evolution.

Multiscale defects engineering offers a promising strategy for synergistically enhancing the thermoelectric and mechanical properties of thermoelectric semiconductors. However, the specific impact of individual defects, in particular precipitation, on mechanical properties remains ambiguous. In this work, the mechanical and thermoelectric properties of Sn1.03- xMnxTe (x = 0-0.30) semiconductors are systematically studied. Mn-alloying induces dense dislocations and Mn nano-precipitates, resulting in an enhanced compressive strength with x increased to 0.15. Quantitative calculations are performed to assess the strengthening contributions including grain boundary, solid solution, dislocation, and precipitation strengthening. Due to the dominant contribution of precipitation strengthening, the yield strength of the x = 0.10 sample is improved by ≈74.5% in comparison to the Mn-free Sn1.03Te. For x ≥ 0.15, numerous MnTe precipitates lead to a synergistic enhancement of strength-ductility. In addition, multiscale defects induced by Mn alloying can scatter phonons over a wide frequency spectrum. The peak figure of merit ZT of ≈1.3 and an ultralow lattice thermal conductivity of ≈0.35Wm-1K-1 are obtained at 873 K for x = 0.10 and x = 0.30 samples respectively. This work reveals thaprecipitation evolution optimizes the mechanical and thermoelectric properties of Sn1.03- xMnxTe semiconductors, which may hold potential implications for other thermoelectric systems.

Exploring the large chemical space in search of thermodynamically stable and mechanically robust MXenes via machine learning.

To effectively utilize MXenes, a family of two-dimensional materials, in various applications that include thermoelectric devices, semiconductors, and transistors, their thermodynamic and mechanical properties, which are closely related to their stability, must be understood. However, exploring the large chemical space of MXenes and verifying their stability using first-principles calculations are computationally expensive and inefficient. Therefore, this study proposes a machine learning (ML)-based high-throughput MXene screening framework to identify thermodynamically stable MXenes and determine their mechanical properties. A dataset of 23 857 MXenes with various compositions was used to validate this framework, and 48 MXenes were predicted to be stable by ML models in terms of heat of formation and energy above the convex hull. Among them, 45 MXenes were validated using density functional theory calculations, of which 23 MXenes, including Ti2CClBr and Zr2NCl2, have not been previously known for their stability, confirming the effectiveness of this framework. The in-plane stiffness, shear moduli, and Poisson's ratio of the 45 MXenes were observed to vary widely according to their constituent elements, ranging from 90.11 to 198.02 N m-1, 64.00 to 163.40 N m-1, and 0.19 to 0.58, respectively. MXenes with Group-4 transition metals and halogen surface terminations were shown to be both thermodynamically stable and mechanically robust, highlighting the importance of electronegativity difference between constituent elements. Structurally, a smaller volume per atom and minimum bond length were determined to be preferable for obtaining mechanically robust MXenes. The proposed framework, along with an analysis of these two properties of MXenes, demonstrates immense potential for expediting the discovery of stable and robust MXenes.

Minimum entropy production in inhomogeneous thermoelectric materials

Due to their potential applications in energy production based on waste heat, direct solar radiation or other energy sources, semiconductor materials have for years attracted the attention of theoretical and experimental researchers. The focus has been on improving the performance of thermoelectric devices through several strategies and special interest has been placed on materials with spatially inhomogeneous transport properties. Inhomogeneity can be achieved in various ways, all of them leading, to a greater or lesser extent, to an improvement of the thermoelectric performance. In this paper, general linear heat and electric charge transport processes in inhomogeneous materials are addressed. The guiding idea followed here is that there exists a relationship between inhomogeneity (structuring), minimum entropy production and performance which may be fruitfully exploited for designing more efficient thermoelectric semiconductor devices. We first show that the stationary states of such materials are minimum global entropy production states. This constitutes an extension of the validity of Prigogine’s minimum entropy principle. The heat and charge transport equations obtained within the framework of classical irreversible thermodynamics are solved to find the stationary profiles of temperature and self-consistent electric potential in a one-dimensional model of a silicon–germanium alloy subjected to an external temperature difference. This allows us to assess the effect of the spatial inhomogeneity on the thermoelectric performance. We find that, regardless of the value of the applied temperature difference, the system may efficiently operate in a regime of minimum entropy production and high efficiency.