Showing papers on "Seebeck coefficient published in 2022"

High figure-of-merit and power generation in high-entropy GeTe-based thermoelectrics

Abstract: The high-entropy concept provides extended, optimized space of a composition, resulting in unusual transport phenomena and excellent thermoelectric performance. By tuning electron and phonon localization, we enhanced the figure-of-merit value to 2.7 at 750 kelvin in germanium telluride–based high-entropy materials and realized a high experimental conversion efficiency of 13.3% at a temperature difference of 506 kelvin with the fabricated segmented module. By increasing the entropy, the increased crystal symmetry delocalized the distribution of electrons in the distorted rhombohedral structure, resulting in band convergence and improved electrical properties. By contrast, the localized phonons from the entropy-induced disorder dampened the propagation of transverse phonons, which was the origin of the increased anharmonicity and largely depressed lattice thermal conductivity. We provide a paradigm for tuning electron and phonon localization by entropy manipulation, but we have also demonstrated a route for improving the performance of high-entropy thermoelectric materials. Description Disordered but efficient Thermoelectric materials, many having relative simple compositions, convert heat into electricity. However, Jiang et al. found that adding more cations into a germanium tellurium–based material stabilized a phase with excellent thermoelectric properties. This high-entropy material has low thermal conductivity due to the cation disordering but improved symmetry that helps maintain good electrical properties. The material was used in several devices that showed a high thermoelectric efficiency. —BG A high-entropy material is an outstanding thermoelectric with a combination of delocalized electrons and localized phonons.

High thermoelectric performance realized through manipulating layered phonon-electron decoupling

Abstract: Thermoelectric materials allow for direct conversion between heat and electricity, offering the potential for power generation. The average dimensionless figure of merit ZTave determines device efficiency. N-type tin selenide crystals exhibit outstanding three-dimensional charge and two-dimensional phonon transport along the out-of-plane direction, contributing to a high maximum figure of merit Zmax of ~3.6 × 10−3 per kelvin but a moderate ZTave of ~1.1. We found an attractive high Zmax of ~4.1 × 10−3 per kelvin at 748 kelvin and a ZTave of ~1.7 at 300 to 773 kelvin in chlorine-doped and lead-alloyed tin selenide crystals by phonon-electron decoupling. The chlorine-induced low deformation potential improved the carrier mobility. The lead-induced mass and strain fluctuations reduced the lattice thermal conductivity. Phonon-electron decoupling plays a critical role to achieve high-performance thermoelectrics. Description A material with high potential Thermoelectic materials convert heat to electricity and are attractive for energy generation or solid-state cooling. Su et al. found that doping tin selenide with chlorine and lead substantially improved the thermoelectric figure of merit over a wide temperature range. This effect was mostly due to an improvement in the material’s deformation potential related to mass and strain fluctuations introduced into the n-type material. Improving the figure of merit in this way is challenging because properties are often intertwined and trying to improve one will often degrade others. —BG Doping tin selenide with lead and chlorine results in a material with high thermoelectric efficiency over a broad temperature range.

Maximizing the performance of n-type Mg3Bi2 based materials for room-temperature power generation and thermoelectric cooling

Abstract: Although the thermoelectric effect was discovered around 200 years ago, the main application in practice is thermoelectric cooling using the traditional Bi2Te3. The related studies of new and efficient room-temperature thermoelectric materials and modules have, however, not come to fruition yet. In this work, the electronic properties of n-type Mg3.2Bi1.5Sb0.5 material are maximized via delicate microstructural design with the aim of eliminating the thermal grain boundary resistance, eventually leading to a high zT above 1 over a broad temperature range from 323 K to 423 K. Importantly, we further demonstrated a great breakthrough in the non-Bi2Te3 thermoelectric module, coupled with the high-performance p-type α-MgAgSb, for room-temperature power generation and thermoelectric cooling. A high conversion efficiency of ~2.8% at the temperature difference of 95 K and a maximum temperature difference of 56.5 K are experimentally achieved. If the interfacial contact resistance is further reduced, our non-Bi2Te3 module may rival the long-standing champion commercial Bi2Te3 system. Overall, this work represents a substantial step towards the real thermoelectric application using non-Bi2Te3 materials and devices.

Maximizing the performance of n-type Mg3Bi2 based materials for room-temperature power generation and thermoelectric cooling

Abstract: Although the thermoelectric effect was discovered around 200 years ago, the main application in practice is thermoelectric cooling using the traditional Bi2Te3. The related studies of new and efficient room-temperature thermoelectric materials and modules have, however, not come to fruition yet. In this work, the electronic properties of n-type Mg3.2Bi1.5Sb0.5 material are maximized via delicate microstructural design with the aim of eliminating the thermal grain boundary resistance, eventually leading to a high zT above 1 over a broad temperature range from 323 K to 423 K. Importantly, we further demonstrated a great breakthrough in the non-Bi2Te3 thermoelectric module, coupled with the high-performance p-type α-MgAgSb, for room-temperature power generation and thermoelectric cooling. A high conversion efficiency of ~2.8% at the temperature difference of 95 K and a maximum temperature difference of 56.5 K are experimentally achieved. If the interfacial contact resistance is further reduced, our non-Bi2Te3 module may rival the long-standing champion commercial Bi2Te3 system. Overall, this work represents a substantial step towards the real thermoelectric application using non-Bi2Te3 materials and devices.

High-entropy (Ca0.2Sr0.2Ba0.2La0.2Pb0.2)TiO3 perovskite ceramics with A-site short-range disorder for thermoelectric applications

Abstract: Novel high-entropy perovskite-type (Ca0.2Sr0.2Ba0.2La0.2Pb0.2)TiO3 (CSBLP) ceramics with cubic structure of Pm-3m space group were successful prepared by solid-state reaction method. Results of XRD, SEM-EDS, HRTEM confirmed a homogeneous distribution and equimolar arrangement of multicomponent cations on the A-site. The high-entropy CSBLP ceramics showed long-range structural order and short-range chemical disorder with widely dispersed nanoscale grains varying sizes of 4-6 nm in the microstructure. Because of increased configurational entropy, the CSBLP ceramic has an enhanced Seebeck coefficient (|S|=272 μV/K at 1073 K) and low thermal conductivity (κ=1.75 W/m•K at 1073 K) when annealed at 1300 °C. This work demonstrates the possibility of effectively reducing thermal conductivity and improving the performance of thermoelectric oxides through high-entropy composition design.

Approach to Determine the Density‐of‐States Effective Mass with Carrier Concentration‐Dependent Seebeck Coefficient

Abstract: Band engineering is an effective strategy to improve the electronic transport properties of semiconductors. In thermoelectric materials research, density‐of‐states effective mass is an undoubted key factor in verifying the band engineering effect and establishing a strategy for enhancing thermoelectric performance. However, estimation of the effective mass is demanding or inaccurate depending on the methods taken. A simple equation is proposed, valid for all degeneracy: Log10 (md*T/300) = (2/3) Log10 (n) − (2/3) [20.3 − (0.00508 × |S|) + (1.58 × 0.967|S|)] that utilizes experimentally determined Seebeck coefficient (S) and carrier concentration (n) to determine the effective mass (md*) at a temperature (T). This straightforward equation, which gives an accurate analysis of the band modulation in terms of md*, is indispensable in designing thermoelectric materials of maximized performance.

Selectively tuning ionic thermopower in all-solid-state flexible polymer composites for thermal sensing

Abstract: There has been increasing interest in the emerging ionic thermoelectric materials with huge ionic thermopower. However, it's challenging to selectively tune the thermopower of all-solid-state polymer materials because the transportation of ions in all-solid-state polymers is much more complex than those of liquid-dominated gels. Herein, this work provides all-solid-state polymer materials with a wide tunable thermopower range (+20~-6 mV K-1), which is different from previously reported gels. Moreover, the mechanism of p-n conversion in all-solid-state ionic thermoelectric polymer material at the atomic scale was presented based on the analysis of Eastman entropy changes by molecular dynamics simulation, which provides a general strategy for tuning ionic thermopower and is beneficial to understand the fundamental mechanism of the p-n conversion. Furthermore, a self-powered ionic thermoelectric thermal sensor fabricated by the developed p- and n-type polymers demonstrated high sensitivity and durability, extending the application of ionic thermoelectric materials.

Selectively tuning ionic thermopower in all-solid-state flexible polymer composites for thermal sensing

Abstract: There has been increasing interest in the emerging ionic thermoelectric materials with huge ionic thermopower. However, it's challenging to selectively tune the thermopower of all-solid-state polymer materials because the transportation of ions in all-solid-state polymers is much more complex than those of liquid-dominated gels. Herein, this work provides all-solid-state polymer materials with a wide tunable thermopower range (+20~-6 mV K-1), which is different from previously reported gels. Moreover, the mechanism of p-n conversion in all-solid-state ionic thermoelectric polymer material at the atomic scale was presented based on the analysis of Eastman entropy changes by molecular dynamics simulation, which provides a general strategy for tuning ionic thermopower and is beneficial to understand the fundamental mechanism of the p-n conversion. Furthermore, a self-powered ionic thermoelectric thermal sensor fabricated by the developed p- and n-type polymers demonstrated high sensitivity and durability, extending the application of ionic thermoelectric materials.

Mediating Point Defects Endows n-Type Bi2 Te3 with High Thermoelectric Performance and Superior Mechanical Robustness for Power Generation Application.

Abstract: Bi2 Te3 -related alloys dominate the commercial thermoelectric market, but the layered crystal structure leads to the dissociation and intrinsic brittle fracture, especially for single crystals that may worsen the practical efficiency. In this work, point defect configuration by S/Te/I defects engineering is engaged to boost thermoelectric and mechanical properties of n-type Bi2 Te3 alloy, which, coupled with p-type BiSbTe, shows a competitive conversion efficiency for the fabricated module. First, as S alloying suppresses the intrinsic B i T e , antisite defects and forms a donor-like effect, electronic transport properties are optimized, associated with the decreased thermal conductivity due to the point defect scattering. The periodide compound TeI4 is afterward adopted to further tune carrier concentration for the realization of an optimal ZT. Finally, an advanced average ZT of 1.05 with ultra-high compressive strength of 230 MPa is achieved for Bi2 Te2.9 S0.1 (TeI4 )0.0012 . Based on this optimum composition, a fabricated 17-pair module demonstrates a maximum conversion efficiency of 5.37% under the temperature difference of 250 K, rivaling the current state-of-the-art Bi2 Te3 modules. This work reveals the novel mechanism of point defect reconfiguration in synergistic enhancement of thermoelectric and mechanical properties for durably commercial application, which may be applicable to other thermoelectric systems.

Carriers: the Less, the Faster

Abstract: Thermoelectric (TE) community has long believed that high TE performance requires an optimal carrier concentration traditionally locating in the range of ~1019 to ~1021 cm−3. Herein, we propose that potential high TE performance might also be achieved at lower carrier concentrations of ~1018 to ~1019 cm−3. At this range, extremely large Seebeck coefficient with low thermal conductivity can be effortlessly obtained. The next step to achieve high ZT values is boosting the carrier mobility. We then propose two aspects for carrier mobility optimization, including the strategies of preparing single crystals, improving crystal symmetry, texturing, controlling microscopic defects, sharpening bands, aligning bands, and modulation doping. We also suggest it rather essential to utilize multiple of the strategies to achieve the significant optimization of carrier mobility. Our proposal will be the important guidance for realizing promising performance in new TE materials as well as revisiting the TE performance for traditional systems.

Giant Thermoelectric Properties of Ionogels with Cationic Doping

Abstract: Although ionic thermoelectric (iTE) materials can have very high thermopower, it is of great significance to develop novel methods to further improve the ionic thermopower and figure of merit (ZTi). Here, significant improvement in the thermopower and thus the ZTi value of an ionogel by cationic doping, is reported. Doping sodium dicyanamide (Na:DCA) into the ionogels of poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) and 1‐ethyl‐3‐methylimidazolium dicyanamide (EMIM:DCA) that is an ionic liquid can greatly enhance the thermopower. This is attributed to the interactions between the doped Na+ cations and DCA– anions, thereby increasing the difference in the mobilities of EMIM+ cations and DCA– anions. Moreover, through the combination with the solid networks engineering by an anti‐solvent to PVDF‐HFP, the PVDF‐HFP/EMIM:DCA ionogel doped with 0.5 mol% Na+ with respect to EMIM+ exhibits an ionic thermopower of 43.8 ± 1.0 mV K–1, ionic conductivity of 19.4 ± 0.3 mS cm–1 and thermal conductivity of 0.183 W m–1 K–1 at the relative humidity of 85% and room temperature. The corresponding ZTi value thus reaches 6.1 ± 0.4, much higher than the previous ZTi records of iTE materials. These ionogels can be used in the iTE capacitors for the thermoelectric conversion.

Theoretical investigation of X2NaIO6 (X= Pb,Sr) double perovskites for thermoelectric and optoelectronic applications

Abstract: The full-potential linearized augmented plane wave (FP-LAPW) method was used to evaluate the structural, optical, electronic, and thermoelectric (TE) characteristics of X2NaIO6 (X = Pb, Sr) cubic double perovskite oxides. Pb2NaIO6 and Sr2NaIO6 revealed the semiconductor behavior with a direct band gap (Eg) of 3.75 eV and 5.48 eV, respectively. Furthermore, the optical parameters like absorption coefficient α(ω), reflectivity R(ω), optical conductivity σ(ω), extinction coefficient k(ω), dielectric constants, and refractive index n(ω) are calculated. Electrical conductivity (σ), figure of merit (ZT), Seebeck coefficient (S), thermal conductivity (k), and power factor (PF) are investigated for their thermoelectric (TE) features by using the Boltz-Trap package. Sr2NaIO6 attained the maximum value of ZT (0.7728) with PF of 206.3. Results of cubic X2NaIO6(X = Pb,Sr) double perovskite oxides revealed their potential application in TE and optoelectronic devices.

High-Temperature Thermoelectric Monolayer Bi₂TeSe₂ with High Power Factor and Ultralow Thermal Conductivity

Abstract: Because of the quantum confinement effect and the interface/surface effect, the band gap of 0.8–1.5 eV for two-dimensional (2D) bismuth-based material is significantly enlarged relative to that of bulk phase materials (∼0.2 eV), which removes the inhibition effect caused by bipolar transport for the Seebeck coefficients of bulk-phase bismuth-based materials at high temperature. Therefore, the 2D bismuth-based materials exhibit huge application prospects in high-temperature thermoelectric (TE) devices, whereas their figure of merits (ZT) need to be further improved. This work reports the thermal and electrical transport properties of 2D Bi2TeSe2, a new Janus Bi2Te3-based material, from the first-principles calculations. Compared with Bi2Se3/Bi2Te3 monolayers and corresponding Janus materials, the Bi2TeSe2 monolayer exhibits a much lower lattice thermal conductivity (κ) of 0.27 W/mK at 900 K because of stronger phonon anharmonicity and higher frequency phonon scattering. In addition, because the energy pockets around the valence band maximum show convergence character, the Seebeck coefficient (SC) of the p-type system is effectively enhanced. Combined with its intrinsic high electron transport properties, a high power factor of 3.48 mW/mK2 at 900 K is obtained for the p-type Bi2TeSe2 monolayer. The ultralow κ and enhanced SC of the Bi2TeSe2 monolayer eventually result in a significant optimal ZT value of 3.45 at 900 K. Thus, our study provides insights into the thermoelectric properties of the Bi2TeSe2 monolayer and may open up an effective avenue for applying bismuth-based materials to a high-temperature TE field.

Microstructurally Tailored Thin β‐Ag ₂ Se Films toward Commercial Flexible Thermoelectrics

Abstract: Aiming to overcome both the structural and commercial limitations of flexible thermoelectric power generators, an efficient room-temperature aqueous selenization reaction that can be completed in air within less than 1 min, to directly fabricate thin β-Ag2 Se films consisting of perfectly crystalline and large columnar grains with both in-plane randomness and out-of-plane [201] preferred orientation, is designed. A high power factor (PF) of 2590 ± 414 µW m-1 K-2 and a figure-of-merit (zT) of 1.2 ± 0.42 are obtained from a sample with a thickness of ≈1 µm. The maximum output power density of the best 4-leg thermoelectric generator sample reach 27.6 ± 1.95 and 124 ± 8.78 W m-2 at room temperature with 30 and 60 K temperature differences, respectively, which may be useful in future flexible thermoelectric devices.

Ultrafast photothermoelectric effect in Dirac semimetallic Cd3As2 revealed by terahertz emission

Abstract: The thermoelectric effects of topological semimetals have attracted tremendous research interest because many topological semimetals are excellent thermoelectric materials and thermoelectricity serves as one of their most important potential applications. In this work, we reveal the transient photothermoelectric response of Dirac semimetallic Cd3As2, namely the photo-Seebeck effect and photo-Nernst effect, by studying the terahertz (THz) emission from the transient photocurrent induced by these effects. Our excitation polarization and power dependence confirm that the observed THz emission is due to photothermoelectric effect instead of other nonlinear optical effect. Furthermore, when a weak magnetic field (~0.4 T) is applied, the response clearly indicates an order of magnitude enhancement on transient photothermoelectric current generation compared to the photo-Seebeck effect. Such enhancement supports an ambipolar transport nature of the photo-Nernst current generation in Cd3As2. These results highlight the enhancement of thermoelectric performance can be achieved in topological Dirac semimetals based on the Nernst effect, and our transient studies pave the way for thermoelectric devices applicable for high field circumstance when nonequilibrium state matters. The large THz emission due to highly efficient photothermoelectric conversion is comparable to conventional semiconductors through optical rectification and photo-Dember effect.

First-principles calculations to investigate structural, elastic, electronic, thermodynamic, and thermoelectric properties of CaPd3B4O12 (B = Ti, V) perovskite

Abstract: This study has explored numerous physical properties of CaPd$_3$Ti$_4$O$_{1}$2 (CPTO) and CaPd$_3$V$_4$O$_{12}$ (CPVO) quadruple perovskites employing the density functional theory (DFT) method. The mechanical permanence of these two compounds was observed by the Born stability criteria as well. The band structure of CPTO reveals a 0.88 and 0.46 eV direct narrow band gap while using GGA-mBJ and GGA-PBE potentials, respectively, which is an indication of its fascinating semiconducting nature. The calculated partial density of states indicates the strong hybridization between Pd-4d and O-2p orbital electrons for CPTO, whereas Pd-4d and V-3d-O-2p for CPVO. The study of the chemical bonding nature and electronic charge distribution graph reveals the coexistence of covalent O-V/Pd bonds, ionic O-Ti/Ca bonds, as well as metallic Ti/V-Ti/V bonding for both compounds. The Fermi surface of CPVO ensures a kind of hole as well as electron faces simultaneously, indicating the multifarious band characteristic. The prediction of the static real dielectric function (optical property) of CPTO at zero energy implies its promising dielectric nature. The photoconductivity and absorption coefficient of CPBO display good qualitative compliance with the consequences of band structure computations. The calculated thermodynamic properties manifest the thermodynamical stability for CPBO, whereas phonon dispersions of CPVO exhibit stable phonon dispersion in contrast to slightly unstable phonon dispersion of CPTO. The predicted Debye temperature ($\theta_D$) has been utilized to correlate its topical features including thermoelectric behaviors. The studied thermoelectric transport properties of CPTO yielded the Seebeck coefficient (186 V/K), power factor (11.9 Wcm$^{-1}$K$^{-2}$), and figure of merit (ZT) value of about 0.8 at 800 K, indicating that this material could be a promising candidate for thermoelectric applications.

Giant and bidirectionally tunable thermopower in nonaqueous ionogels enabled by selective ion doping

Abstract: Ionic thermoelectrics show great potential in thermal sensing owing to their ultrahigh thermopower, low cost, and ease in production. However, the lack of effective n-type ionic thermoelectric materials seriously hinders their applications. Here, we report giant and bidirectionally tunable thermopowers within an ultrawide range from −15 to +17 mV K−1 in solid ionic liquid–based ionogels. Particularly, a record high negative thermopower of −15 mV K−1 is achieved in the ternary ionogel, rendering it among the best n-type ionic thermoelectric materials under the same condition. A thermopower regulation strategy through ion doping to selectively induce ion aggregates to enhance ion-ion interactions is proposed. These selective ion interactions are found to be decisive in modulating the sign and magnitude of the thermopower in the ionogels. A prototype wearable device integrated with 12 p-n pairs is demonstrated with a total thermopower of 0.358 V K−1, showing promise for ultrasensitive thermal detection.

A novel high-entropy perovskite ceramics Sr0.9La0.1(Zr0.25Sn0.25Ti0.25Hf0.25)O3 with low thermal conductivity and high Seebeck coefficient

Abstract: In this work, a novel high-entropy n -type thermoelectric material Sr 0.9 La 0.1 (Zr 0.25 Sn 0.25 Ti 0.25 Hf 0.25 )O 3 with pure perovskite phase was prepared using a conventional solid state processing route. The results of TEM and XPS show that various types of crystal defects and lattice distortions, such as oxygen vacancies, edge dislocations, in-phase rotations of octahedron and antiparallel cation displacements coexist in this high-entropy ceramic. At 873 K, the high-entropy ceramics showed both a low thermal conductivity (1.89 W/m/K) and a high Seebeck coefficient (393 μV/K). This work highlights a way to obtain high-performance perovskite-type oxide thermoelectric materials through high-entropy composition design.