Large Seebeck Coefficient Research Articles

Achieving low thermal conductivity and high quality factor in sextuple-doped TiS2

Transition-metal dichalcogenide TiS2 stands out as a sustainable candidate for room- and medium-temperature thermoelectric materials due to its affordability, non-toxicity, eco-friendly nature and use of non-critical elements. However, its light element compositional nature results in a large thermal conductivity, which is the main limitation of the thermoelectric performance of TiS2. Here, we report a multi-element doping strategy by incorporating equivalent (Se, Zr) elements and introducing higher-valence (Nb, Ta) and lower-valence (Y, La) elements in pairs to minimize its lattice thermal conductivity, κlat. The findings indicate a nearly 50% decrease in κlat across the entire temperature range, attributed to the presence of strong point-defect scattering after multi-element doping. Additionally, we observed a reduced dependency of κlat on temperature in multi-element doped TiS2, as point defects can effectively scatter phonons at room temperature. As a result, the multi-element doped TiS2 attained its highest ZT value of approximately 0.4 at 625 K. Incorporating higher-valence and lower-valence elements in pairs proves to be an effective method for decreasing lattice thermal conductivity without compromising too much of its large Seebeck coefficient.

Semiconducting Heusler Compounds beyond the Slater-Pauling Rule

Heusler compounds with semiconducting properties represent an important class of functional materials. Usually, research on these systems is guided by simple electron-counting rules, such as the Slater-Pauling principle. Here, we report on the discovery of Heusler-type semiconductors, significantly deviating from the Slater-Pauling rule. We theoretically predict the occurrence of nonmagnetic semiconducting ground states in various highly off-stoichiometric full-Heusler alloys, where self-substitution leads to a band-gap opening. This unexpected trend is confirmed experimentally by thermoelectric transport measurements on a multitude of Fe2−2xV1−xAl1+3x samples with up to 20% substitution of Fe and V atoms. The band-gap opening leads to an exceptionally large Seebeck coefficient in p-type Fe2VAl thermoelectrics, previously limited by bipolar conduction and low-density-of-states effective mass. Consequently, our work presents a paradigm to tune the band gap of Heusler compounds by self-substitution and introduces a hitherto unexplored class of semiconductors with exceptional thermoelectric properties, offering significant potential for advancements in energy science and sustainable-energy technologies. Published by the American Physical Society 2024

Understanding the Anomalous Thermoelectric Behavior of Fe-V-W-Al-Based Thin Films.

We investigated the thermoelectric and thermal behavior of Fe-V-W-Al-based thin films prepared using the radio frequency magnetron sputtering technique at different oxygen pressures (0.1-1.0 × 10-2 Pa) and on different substrates (n, p, and undoped Si). Interestingly, at lower oxygen pressure, formation of a bcc-type Heusler structure was observed in deposited samples, whereas at higher oxygen pressure, we have noted the development of an amorphous structure in these samples. Our findings indicate that the moderately oxidized Fe-V-W-Al amorphous thin film deposited on the n-Si substrate possesses a large magnitude of S ∼ -1098 ± 100 μV K-1 near room temperature, which is almost double the previously reported value for thin films. Additionally, the power factor (PF) indicated an enormously large value of ∼33.9 mW m-1 K-2 near 320 K. The thermal conductivity of the amorphous thin film is also found to be 2.75 Wm-1 K-1, which is quite lower compared to bulk alloys. As a result, the maximum figure of merit is estimated to be extremely high, i.e., ∼3.9 near 320 K, which is among one of the highest reported values so far. The anomalously large value of Seebeck coefficient and PF has been ascribed to the unusual composite effect of the metallic amorphous oxide phase and insulating substrate possessing a large Seebeck coefficient.

First-principles investigation of structural, electronic, optical and thermoelectric performance of stable inorganic double perovskites A2AlAgBr6 (A=K, Rb, Cs) for energy harvesting

In this work, the structural, electronic, optical and thermoelectric properties of Cs2AlAgBr6, K2AlAgBr6 and Rb2AlAgBr6 have been investigated using WIEN2k code. All the three double perovskites show stability. The stability is confirmed by calculating their formation energy, tolerance factor and molecular dynamic simulations. The electronic properties revealed the understudy compounds as semiconductors of direct band gap of 2.62, 2.61 and 2.59 eV for Cs2AlAgBr6, K2AlAgBr6 and Rb2AlAgBr6, respectively. The absorption band of our compounds is mostly in the ultraviolet energy range which is particularly significant for optoelectronic devices. The studied double perovskites exhibit a large Seebeck coefficient and electrical conductivity, which is significant for the high figure of merit. These properties make them particularly suitable for thermoelectric (TE) devices and other photovoltaic applications, as their high figure of merit at low temperatures opens up new possibilities for these materials.

A theoretical investigation on the structure stability, electronic structures, optical properties, and transport properties of Zintl compounds CsZn4P3 and CsZn4As3

The present study investigates the structure stability, electronic structures, and optical properties of Zintl compounds CsZn4P3 and CsZn4As3 by first-principles calculations. An assessment of the phonon dispersion curves and elastic constants indicate both dynamic and mechanical stability for the both compounds. By employing the HSE06 hybrid functional, both compounds display direct bandgap with widths of 0.93 eV for CsZn4P3 and 0.66 eV for CsZn4As3. Furthermore, an analysis of the dielectric constant, refractive index, extinction coefficient, and energy loss as functions of photon energy is conducted to study the optical properties. Based on the semi-classical Boltzmann transport theory and the Slack's equation, a large Seebeck coefficient and minimum lattice thermal conductivity are obtained for CsZn4As3, which result in a figure of merit value of 0.79 at 700 K. These findings underscore the potential of CsZn4As3 as a promising candidate for future research and development in the realm of thermoelectric materials.

First principle insights on optoelectronic, mechanical, and thermoelectric properties of double perovskites Li2ScAu (Br/I)6 for energy harvesting applications

Li-based double perovskites (DPs) are extensively studied due to their potential applications for solar cells and thermoelectric devices. In the current paper, I have explored the electronic, optical, transport, and mechanical properties of Li2ScAu (Br/I)6 by density functional theory (DFT) based calculations. The tolerance factor and Born Criteria have been assumed for structural and mechanical stability. In contrast, energy and phonons band structures are examined for thermodynamic and dynamic (Lattice vibration) stabilities. The band gaps of 1.96 eV and 1.42 eV for Li2ScAuBr6 and Li2ScAuI6 fall the absorption bands in the visible zone. The optical characteristics are addressed in the energy range of 0–5.0 eV. The low lattice thermal conductivity, large Seebeck coefficient, and electrical conductivity enhance the figure of merit (ZT) scale that increasse their importance for thermoelectric generators.

Effective Self‐Powered Semimetal TaTe2 Photodetector with the Thermal Localization Photothermoelectric Effect from Ultraviolet to Mid‐Infrared Range

AbstractUltra‐broadband photodetectors based on semimetal crystals have recently become popular because of their gapless band structures. In particular, semimetal crystals have large carrier mobility or high Seebeck coefficient; this almost eliminates the possibility of using semimetal crystals as photodetectors. In addition, a larger temperature gradient can cause photocurrent generation based on the photothermoelectric effect. Surprisingly, the TaTe2 crystal has a huge absorption coefficient (≈104 cm−1), a minimal specific heat (≈0.172 J g−1 K−1), and a low thermal conductivity (0.3 W m−1 K−1), which is beneficial for generating a high photothermal conversion efficiency of 30.2%, despite its small Seebeck coefficient, and achieving a large temperature gradient occurs for the heat generated by external illumination. Herein, the possibility of photoresponse based on the TaTe2 detector is explored, which has a low carrier mobility (≈10 cm2 V−1 s−1) and a small Seebeck coefficient (≈7.1 µV K−1). The self‐powered TaTe2 photodetector can also provide a competitive photoresponse range from 355 to 2715 nm and exhibit a maximum responsivity of 1.1 mA W−1 with a detectivity of 4.7 × 108 Jones at 455 nm. This study provides a new design scheme and operating mechanism for semimetal photodetectors and enriches semimetal crystal photodetectors.

Thermoelectric performance of Ag2GeX3 (X = S, Se, Te) with intrinsically low lattice thermal conductivity: A first principles study

Low lattice thermal conductivity is one of the key factor for excellent thermoelectric performance of materials. In this work, we have systematically studied the thermoelectric properties of Ag2GeX3 (X = S, Se, Te) by first-principles calculations in combination with Boltzmann transport theory. In terms of phonon transmission performance, due to the low frequency of acoustic phonons, strong coupling between low-frequency optical phonons and acoustic phonons, and relatively strong anharmonicity, Ag2GeX3 (X = S, Se, Te) exhibits extremely low lattice thermal conductivity of 0.30 Wm−1K−1, 0.28 Wm−1K−1 and 0.65 Wm−1K−1 at room temperature, respectively. At the same time, Ag2GeX3 (X = S, Se, Te) also exhibits good electrical transport performance. The appropriate band gap and high slope of electronic density of states (DOS) near the Fermi level result in a large Seebeck coefficient of the materials. As a result, the optimal ZT values of p(n)-type Ag2GeX3 (X = S, Se, Te) are 1.4(1.2), 2.2(0.7), and 0.9(0.7) at 800 K, respectively. These results demonstrate outstanding thermoelectric performance of Ag2GeSe3 for energy conversion applications.

Divacancy and resonance level enables high thermoelectric performance in n-type SnSe polycrystals

N-type polycrystalline SnSe is considered as a highly promising candidates for thermoelectric applications due to facile processing, machinability, and scalability. However, existing efforts do not enable a peak ZT value exceeding 2.0 in n-type polycrystalline SnSe. Here, we realized a significant ZT enhancement by leveraging the synergistic effects of divacancy defect and introducing resonance level into the conduction band. The resonance level and increased density of states resulting from tungsten boost the Seebeck coefficient. The combination of the enhanced electrical conductivity (achieved by increasing carrier concentration through WCl6 doping and Se vacancies) and large Seebeck coefficient lead to a high power factor. Microstructural analyses reveal that the co-existence of divacancy defects (Se vacancies and Sn vacancies) and endotaxial W- and Cl-rich nanoprecipitates scatter phonons effectively, resulting in ultralow lattice conductivity. Ultimately, a record-high peak ZT of 2.2 at 773 K is achieved in n-type SnSe0.92 + 0.03WCl6.

Effect of Ni-Doping on Seebeck Coefficient of LaCoO<sub>3</sub> System

The aim of this study is discussing the results achieved on undoped and Ni-doped bulk LaCoO3 samples synthesized by solid-state reaction. The crystal structures of the samples were analyzed by x – ray diffraction (XRD) and Rietveld refinement of the XRD patterns was used to test the quality of the samples, the results of this procedure confirmed a single phase of LaCo1-xNixO3 for (x=0 and 0.05) with rhombohedral crystal structure (space group :). The main interest in this class of materials is the possibility of improving the values of Seebeck coefficient and electrical resistivity through chemical doping. The Seebeck coefficient and electrical resistivity were investigated from room temperature (RT) to 450 K, near RT the LaCoO3 system showed a large negative Seebeck coefficient, but it changed to positive value with increasing temperature while the LaCo0.95Ni0.05O3 composition showed a positive Seebeck coefficient throughout all the temperature range. Hence, within this study the Ni substitution led to decrease the electrical resistivity of the samples to one order of magnitude as a result of the partial substitution of Co3+ in LaCoO3 by Ni2+. LaCoO3 was chosen for this thermoelectric test because cobalt oxides have extensive applications.

Enhanced thermoelectric performance of W18O49/ZnO composite for waste heat recovery with induced high weighted mobility

Zinc Oxide (ZnO) exhibits a significant Seebeck coefficient, making it a promising candidate for thermoelectric energy harvesting. This study explores composite materials comprising xW18O49/(1-x)ZnO fabricated through conventional sintering at 1150°C, with x varying from 0 to 0.3. Incorporating a highly conductive secondary phase into the ZnO matrix enhances conductivity by 28 times, reaching 111.4 Scm−1 at 800°C, while maintaining 83 % of the pristine sample's Seebeck coefficient. Notably, the power factor improves to 3.8 mWK−2m−1 for the x = 0.1 sample, representing a 19 times heightening over unmodified ZnO ceramic. Additionally, these composites exhibit high weight mobility, indicating rapid electronic responses. As a result, the ZT value increases by 500 %, reaching 0.15 at 800°C for the x = 1 sample. This study presents a novel approach to fabricating high-power-factor thermoelectric materials by integrating highly conductive oxides into matrices with large Seebeck coefficients.

Four-Phonon Enhanced the Thermoelectric Properties of ScSX (X = Cl, Br, and I) Monolayers.

Recently, the FeOCl-type two-dimensional materials have attracted significant attention owing to their versatile applications in fields such as thermoelectricity and photocatalysis. This study aims to systematically investigate the thermoelectric properties of ScSX (X = Cl, Br, and I) monolayers by a combination of the first-principles calculations and the machine-learning interatomic potential approach. These monolayers are indirect semiconductors with band gaps of 3.22 (ScSCl), 3.27 (ScSBr), and 2.87 eV (ScSI), respectively. The lattice thermal conductivity is decreased by 25.72% (20.90%), 44.05% (40.00%), and 30.96% (34.76%) for ScSCl, ScSBr, and ScSI along the x-axis (y-axis) when the four-phonon scattering is introduced, indicating its important role in phonon transport. Anharmonic phonon scattering yields high Grüneisen parameter and scattering rate values, hence causing these low lattice thermal conductivities. Additionally, the large Seebeck coefficients and electrical conductivities of n-type doped ScSX monolayers contribute to their excellent power factors (24.69, 25.66, and 24.99 mW/K2·m for ScSCl, ScSBr and ScSI at 300 K, respectively). Based on the excellent power factor and low thermal conductivity, the maximum values of the figure of merit are calculated to be 2.68, 3.39, and 3.21 for ScSCl, ScSBr, and ScSI monolayers at 700 K, respectively. Our research provides valuable insights into the phonon thermal transport of ScSX monolayers and suggests a promising approach to address high-order anharmonicity.

High-throughput approach to explore cold metals for electronic and thermoelectric devices

Cold metals with an energy gap around the Fermi level have been shown a great potential for reducing the power dissipation of transistors and diodes. However, only a limited number of 2D cold metals have been studied. In this work, we explored 3D cold metals through a systematic material search and found 252 types in the database. We performed first-principles calculations to investigate the conductance and work functions of 30 cold metals for material selection. Additionally, we studied the thermoelectric properties of four typical cold metals, which possess much larger Seebeck coefficients and figure-of-merits than conventional metals, by one and two orders of magnitude, respectively. Specifically, we constructed a monolayer MoS2 transistor with a cold metal contact of ZrRuSb. Our quantum transport simulations indicate that cold metal contacted MoS2 FETs exhibit a subthreshold swing smaller than 60 mV decade−1 over four decades, and on-state currents over 1 mA μm−1 are achieved at a supply voltage of 0.5 V. Our research provides a theoretical foundation and material basis for exploring 3D cold metals in developing electronic and thermoelectric devices.

Anomalous thermal transport and high thermoelectric performance of Cu-based vanadate CuVO3

Thermoelectric (TE) conversion technology, capable of transforming heat into electricity, is critical for sustainable energy solutions. Many promising TE materials contain rare or toxic elements, so the development of cost-effective and eco-friendly high-performance TE materials is highly urgent. Herein, we explore the thermal transport and TE properties of transition metal vanadate CuVO3 by using first-principles calculation. On the basis of the unified theory of heat conduction, we uncover the hierarchical thermal transport feature in CuVO3, where wave-like tunneling makes a significant contribution to the lattice thermal conductivity (κl) and results in the anomalously weak temperature dependence of κl. This is primarily attributable to the complex phononic band structure caused by the heterogeneity of Cu–O and V–O bonds. Simultaneously, we report a high power factor of 5.45 mW·K−2·m−1 realized in hole-doped CuVO3, which arises from a high electrical conductivity and a large Seebeck coefficient enabled by the multiple valleys and large electronic density of states near the valence band edge. Impressively, the low κl and the high power factor make p-typed CuVO3 have ZT of up to 1.39, with the excellent average ZT above 1.0 from 300 to 600 K, which is superior to most reported Cu-based TE materials. Our findings suggest that the CuVO3 compound is a promising candidate for energy conversion applications in innovative TE devices.

Computational study of stability, photovoltaic, and thermoelectric properties of new inorganic lead-free halide perovskites

Abstract Due to their rich and extraordinary properties, halide perovskites have gained attention over time for their applications in thermoelectric and solar cells. Here, several physical properties (stability, photovoltaic, and thermoelectric) of inorganic halide perovskites XZnI3 (X = Na, K, Rb, Cs) are predicted using the density functional theory (DFT) within the Wien2k code. The optimization of structural parameters has been calculated using PBE-GGA approach. The tolerance factor, Born criteria, phonon dispersion, and negative formation energy show the formation and stability of these studied materials in the ideal cubic structure. Additionally, the modified Becke-Johnson method is applied for optoelectronic and transport properties. All compounds exhibit the nature of indirect band gap semiconductors with better absorption in the visible and ultraviolet regions 10^{5} \textrm {cm}^{-1})$ ?> . The transport properties present high electrical conductivity, large Seebeck coefficient, and good (PF, ZT) factors for all these materials. Finally, all these properties of inorganic halide perovskites open up new possibilities for efficient applications in thermoelectric and solar cells.

Unveiling the DFT perspectives on structural, elastic, optoelectronic, and thermoelectric properties of zirconate perovskites XZrO3 (X = Ca, Sr, Ba)

A thorough comparative study of lead free zirconate perovskite XZrO3 (X = Ca, Sr, Ba) is carried out employing WIEN2k which is a density functional theory based code. A good agreement between reported synthesis and the theoretical results is observed. BaZrO3 can be inferred as the most stable compound among XZrO3 (X = Ca, Sr, Ba) as its ground state energy is lowest. According to the Burn-Haun criterion, the compounds under research are mechanically stable. The ductile nature, anisotropy, and reasonable resistance to deformation in response to external stress are observed. The semiconducting nature of the compounds is observed having indirect band gaps with values of 3.25 eV, 3.71 eV, and 3.80 eV. Exceptional optical absorption peaks for the investigated compounds can be observed in UV region (around 5.0 eV) which suggests their numerous optoelectronic applications within UV. XZrO3 (X = Ca, Sr, Ba) are active optical materials as their refractive inrdex n(ω) occurs in the range of 1.0 and 2.0. Thermoelectric properties of these compounds are also very promising since the large Seebeck coefficients (∼2250–2700 μV/K), large power factor values (∼1011 W/mK2s), and figure of merits are very close to the unity are observed. The mechanical stability and ductility, and the appealing optical and thermoelectric properties of the examined compounds persuade us that these compounds may play a significant role for numerous industrial applications like solar cells, LEDs, sensors, thermoelectric generators and other energy conversion devices in the future.

Phonon-drag in a graphite channel buried in diamond

While the phonon-drag effect can induce large Seebeck coefficients, it is associated with large mean free path phonons present in the vicinity of the maximum in temperature of the lattice thermal conductivity. In this paper, we initiate a new route by searching for the mutual drag between the electron and phonon-drag gases at the interface between two different media. In that respect, the temperature studies of the conductance and Seebeck coefficient of a model system consisting of an electrically conductive graphitic channel buried beneath the surface of a diamond crystal are shown. The observed behaviour is very similar to that of graphite, with a typical negative peak associated with the phonon-drag effect. Interestingly, this phonon-drag peak of the buried graphitic channel appears at a significantly higher temperature than that in pure graphite.

A study of the effect of cerium ion doping concentration on the structural, electrical, and thermoelectric properties of CaMnO3 nanoparticles

Abstract Universally, energy loss in the form of heat is predominant and this heat is irrecoverable waste heat that leads to global warming. Clean, green, eco-friendly, cost-effective, and renewable energy sources are the possible solutions for this energy crisis and global warming issues. Thermoelectric power generation is a promising technology by converting this irrecoverable waste heat directly into electricity without any greenhouse gas emission. Nanostructured CaMnO3 at various cerium concentrations have been successfully prepared by sol–gel hydrothermal method followed by annealing and sintering. Pure and doped samples were systematically characterized by DSC, powder XRD, RAMAN, SEM with EDAX and FTIR spectroscopy. Electrical and thermoelectrical measurements were carried out on the sintered pellets. The XRD analyses confirmed the formation of orthorhombic perovskite structure for all the samples and the average particle size lies in the range of 50–60 nm. FTIR analysis shows the presence of CaMnO3 nanoparticles without any impurities. The temperature dependence of physical properties was performed and analyzed between room temperature and 600 °C. Electrical resistivity strongly depends on the nature of substituent ions and negative values indicate that the electrons are major charge carriers. Large Seebeck coefficient value and high-power factor make Ca1−x Ce x MnO3 an efficient thermoelectric material for energy storage applications.

Extremely large Seebeck coefficient of gelatin methacryloyl (GelMA)-based thermogalvanic cells by the dual effect of ion-induced crystallization and nanochannel control

The quasi-solid state thermogalvanic cells (TGCs) have been extensively investigated due to their high Seebeck coefficient (S) and suitability for wearable power generation. However, the influence of hydrogel nanostructure on Seebeck coefficient remains underexplored. In this study, biocompatible TGCs based on gelatin methacryloyl (GelMA) are fabricated via a fast-photocrosslinking process. Moreover, guanidium chloride (GdmCl) salts are directly introduced into the TGCs to enhance the Seebeck coefficient via ion-induced crystallization in the p-type FeCN63−/FeCN64− redox system. Small angle X-ray scattering reveals controlled GelMA hydrogel mesh size adjusting the amount of GdmCl, leading to improved intermolecular interactions between the guanidium cations and GelMA polymer. The optimized p-type Seebeck coefficient reaches an unprecedented 21.6 mV K−1, which is the highest thus far reported in the context of the TGC system. Furthermore, a prototype wearable thermoelectric generator (TEG) with an output voltage of 1.6 V under a temperature difference (ΔT) of 9 °C is able to power an LED directly without requiring an additional voltage booster. In brief, the dual effect of ion-induced crystallization and nanochannel control substantially enhances the Seebeck coefficient of the TGC, thereby offering a promising strategy for enhancing the performance of low-grade thermal energy harvesting wearable TEGs.

Ba4Cd2Ge2Te9: A Promising Infrared Functional Crystal with Large Birefringent and Photoluminescence Properties

Herein, a new Cd-based telluride Ba4Cd2Ge2Te9 was successfully synthesized and characterized, which was first identified in the Ba-Cd-Ge-Te system. It crystallizes in the Pbcm space group and its structure features infinite [Cd2Ge2Te9]8- chains, with Ba2+ filling in the interstitial space to balance the charge. The fluorescence spectrum indicates that the title compound generates purple-emission the range of 415-459nm under the 300nm excitation, with a peak lifetime of about 1.18ns at 436nm. In addition, first-principles calculations show that Ba4Cd2Ge2Te9 has a birefringence of 0.298@2090nm, which is determined by the superposition of the polarization of the terminal Te atom and Ge2Te6 unit. Thermoelectricity measurements show that the title compound possesses a large Seebeck coefficient (655 μV K−1 @300K) and a low thermal conductivity (0.87Wm-1 K-1 @300K).