Large Seebeck Coefficient Research Articles

Enhanced high-temperature stability of indium tin oxide - Indium oxide thermocouples by two-step annealing

The complex internal structure of the aero-engine and the high-temperature, high-pressure, and high-speed airflow make it difficult to measure the internal temperature. Indium tin oxide (ITO) and In2O3 films have been studied for their application in high-temperature thermocouples and strain gauges. Due to their large Seebeck coefficient and high-temperature stability, ceramic thin-film thermocouples are expected to be used at high-temperature measure. In this paper, ITO-In2O3 thermocouples were fabricated by magnetron sputtering. Besides, the electrical properties of the air-annealed and two-step nitrogen-annealed thermocouples were compared, including the repeatability of thermoelectric response after multiple thermal cycles and the drift rate during the high-temperature duration. The microstructure and electrical conductivity of both the as-deposited and post-annealed ceramic thin films were tested respectively. The result shows that the resitivity and Seebeck coefficient of the thin films annealed in nitrogen is reduced, but the stability at high temperature is greatly improved.

Enhanced thermoelectric properties of heavy-fermion compounds YbxCeySmzIr2Zn20 ( x+y+z=1 )

Thermoelectric materials hold tremendous promise for advances in fundamental science and practical applications, particularly for robust electricity generation in extreme and remote environments. Despite this, for most materials the energy conversion efficiency is limited by the proportionality between the electrical and thermal conductivities and small values of the Seebeck coefficient for metals. It was previously reported that the heavy-fermion compound ${\mathrm{YbIr}}_{2}{\mathrm{Zn}}_{20}$ exhibits large Seebeck coefficient [E. Mun et al., Phys. Rev. B 86, 115110 (2012)] and thermoelectric figure of merit $ZT$ at 35 K [K. Wei et al., Sci. Adv. 5, eaaw6183 (2019)]. This behavior is primarily associated with strong hybridization between the $f$- and conduction electron states. Here, we seek to improve the thermoelectric properties through chemical substitution on the Yb site using Ce and Sm. By surveying different levels of substitution, we find that the thermoelectric properties vary strongly with the $f$-element ratio. This confirms that electronic hybridization dominates the thermoelectric properties and clarifies directions for optimizing these materials for applications. We also investigate the impact of the disorder on the thermal conductivity, where we find only weak variation with lanthanide content.

Facile fabrication of Cu2O nanowire networks with large Seebeck coefficient for application in flexible thermoelectrics

The development of thermoelectrical nanowires and nanowire networks is crucial for application in self-powered electronics and flexible heat-to-power conversion devices. While Cu2O is a perspective p-type thermoelectric material, its research is mostly focused on the investigation of the properties of thin films or rigid cement composites with Cu2O powder fillers. In this work, Cu2O nanowire networks were fabricated by a simple technique and their thermoelectrical properties were investigated for the first time. Cu2O nanowire networks were obtained by annealing prefabricated CuO nanowire networks in an inert atmosphere at low pressure of 0.2 Torr. After annealing, nanowire networks showed a complete transition of CuO phase to Cu2O. Seebeck coefficient of Cu2O nanowire networks reached 2000 μV K−1. The estimated power factor of the Cu2O networks was found to be comparable with the Seebeck coefficient values of the state-of-the-art Cu2O thin films. The demonstrated in this work simple low-cost method for the fabrication of Cu2O nanowire networks illustrates the potential of this material for further applications in flexible thermoelectric devices.

Electronic, optical and thermoelectric properties of halide double perovskites Rb2AgInX6 (X = Cl, Br, I)

In the last decades, lead-based perovskites have been substantially investigated due to their superior efficiency in photovoltaics. However, owing to the harmful effect of lead, the search for other environmentally friendly materials is vital. Recently, halide double perovskites have gained attention due to their environmental friendliness and potential applications in solar cells and thermoelectric devices. The energy gap, optical and thermoelectric parameters of Rb2AgIn(Cl/Br/I)6 halide double perovskites compounds were investigated using Wien2k and BoltzTraP2 code based on DFT. The energy gap was 2.62 eV, 1.74, and 0.56 eV for Rb2AgIn(Cl/Br/I)6 at the Γ-points, which were direct bandgaps. More states were localized near the upper valence band, closer to the fermi energy, than near the lower conduction band, suggesting that Rb2AgIn(Cl/Br/I)6 was p-type. The fundamental edge of absorption arises at 2.48 eV, 1.67 eV, and 0.45 eV for Rb2AgIn(Cl/Br/I)6. The optical bandgaps calculated using the Tauc plot were 2.59 eV, 1.7 eV, and 0.49 eV for Rb2AgIn(Cl/Br/I)6. The first absorption band illustrates that these halide double perovskite compounds show high in the visible spectrum, with maximum absorption in the UV region. The Seebeck coefficient was positive, indicating the presence of p-type carriers. The calculated hole concentrations at room temperature were 3.08 × 1020 cm−3, 1.72 × 1020 cm−3, and 8.37 × 1019 cm−3 for Rb2AgInCl6, Rb2AgInBr6 and Rb2AgInI6 respectively. Large Seebeck coefficients with high thermoelectric efficiencies (greater than unity at room temperature) were observed for these halide double perovskites compounds.

Phase transition enhanced thermoelectric performance for perovskites: The case of AgTaO3

In general, perovskite materials, such as AgTaO3, can exhibit complex structural phase transitions when the temperature changes. Different phase structures may show distinct thermoelectric properties. However, the effects of phase transition on the thermoelectric performance of AgTaO3 have yet to be systematically investigated. Thus, in this work, the electronic structures and thermoelectric properties of the p-type AgTaO3 in various phase structures are investigated by utilizing first-principles calculations and semi-classical Boltzmann transport theory. The results show that the p-type AgTaO3 in the cubic phase shows a superior power factor because the cubic phase possesses a large Seebeck coefficient and intermediate electrical conductivity. The calculated thermoelectric performance is consistent with the predictions and explanations from the analyses of the electronic structures. When the p-type AgTaO3 is transformed from the tetragonal phase to the cubic phase, its power factor is tripled, suggesting that a suitable phase transition can improve the thermoelectric properties of perovskites.

Pulse Electrochemically Driven Multilayer Assembly of Single‐Walled Carbon Nanotube/Polypyrrole/Tellurium Composite Films for Ultra‐High‐Performance Flexible Thermoelectric Applications

AbstractAlthough several efforts were made to develop high‐performance thermoelectric (TE) composites by a combination of single‐walled carbon nanotubes (SWCNTs) with a high conductivity and tellurium (Te) with a large Seebeck coefficient, only a very limited advance has been achieved because of their intrinsic interfacial incompatibility. In this work, a range of SWCNT/polypyrrole (PPy)/Te flexible composite films are prepared through sequentially pulse electrodepositing PPy and Te over the prefabricated SWCNT membrane electrode, where both the introduction of the PPy sandwich layer and the adoption of two pulse electrodepositions play a vital role in ameliorating the TE performance of the composites via the synergic optimization of an interfacial engineering. Consequently, the best power factor for the optimal SWCNT/PPy/Te composite film reaches up to 1602.4 ± 87.6 µW m−1 K−2 at 300 K, which hits the record for the p‐type PPy‐based TE composites. Moreover, the five‐leg flexible thermoelectric generators assembled with the optimal film harvest an output power of 1512.5 nW at the applied temperature difference of 22.4 K. This work suggests that the multilayer assembly technology driven by pulse electrochemistry is a feasible and effective tactic for architecting high‐performance flexible TE films.

Theoretical Prediction of Thermoelectric Performance for Layered LaAgOX (X = S, Se) Materials in Consideration of the Four-Phonon and Multiple Carrier Scattering Processes.

Inspired by the experimental achievement of layered LaCuOX (X = S, Se) with superior thermoelectric (TE) performance, the TE properties of Ag-based isomorphic LaAgOX are systemically investigated by the first-principles calculation. The LaAgOS and LaAgOSe are direct semiconductors with wide bandgaps of ≈2.50 and ≈2.35eV. Essential four-phonon and multiple carrier scattering mechanisms are considered in phonon and electronic transport calculations to improve the accuracy of the figure-of-merit (ZT). The p-type LaAgOX (X = S, Se) shows excellent TE performance on account of the large Seebeck coefficient originated from the band convergency and low thermal conductivity caused by the strong phonon-phonon scattering. Consequently, the optimal ZTs along the out-of-plane direction decrease in the order of n-type LaAgOSe (≈2.88) > p-type LaAgOSe (≈2.50) > p-type LaAgOS (≈2.42) > n-type LaAgOS (≈2.27) at 700K, and the optimal ZTs of ≈1.16 and ≈1.29 are achieved for p-type LaAgOS and LaAgOSe at the same temperature. The present work would provide a deep insight into the phonon and electronic transport properties of LaAgOX (X = S, Se), but also could shed light on the way for the rational design of state-of-the-art heteroanionic materials for TE application.

Thermoelectric Response Enhanced by Surface/Edge States in Physical Nanogaps.

Current solid-state thermoelectric converters have poor performance, which typically renders them useless for practical applications. This problem is evidenced by the small figures of merit of typical thermoelectric materials, which tend to be much smaller than 1. Increasing this parameter is then key for the development of functional devices in technologically viable applications that can work optimally. We propose here a feasible and effective design of new thermoelectric systems based on physical gaps in nanoscale junctions. We show that, depending on the type of features, i.e., the character of surface/edge states, on both sides of the gap, it is possible to achieve high figures of merit. In particular, we show that, for configurations that have localized states at the surfaces/edges, which translate into sharp resonances in the transmission, it is possible to achieve large Seebeck coefficients and figures of merit by carefully tuning their energy and their coupling to other states. We calculate the thermoelectric coefficients as a function of different parameters and find non-obvious behaviors, such as the existence of a certain coupling between the localized and bulk states for which these quantities have a maximum. The highest Seebeck coefficients and figures of merit are achieved for symmetric junctions, which have the same coupling between the localized state and the bulk states on both sides of the gap. The features and trends of the thermoelectric properties and their changes with various parameters that we find here can be applied not only to systems with nanogaps but also to many other nanoscale junctions, such as those that have surface states or states localized near the contacts between the nanoscale object and the electrodes. The model presented here can, therefore, be used to characterize and predict the thermoelectric properties of many different nanoscale junctions and can also serve as a guide for studying other systems. These results pave the way for the design and fabrication of stable next-generation thermoelectric devices with robust features and improved performance.

The thermoelectric power function of new composite Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)/carbonyl iron films: A new exploration

In this work, carbonyl iron particles (CIR) have been mixed with a semi-metallic poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (designated PP) to produce a composite of PP/CIR films with a high Seebeck coefficient as a trail to overcome the low thermoelectric (TE) properties of PP polymer. The good distribution of CIR particles in the PP template leads to improving the TE performance. The reduction in the electrical conductivity (σ) is detected with the CIR content, with the lowest σ of 54.782 ± 6.803 Scm−1 at 50 wt% which is ∼ 5.5 times smaller than that of PP. The Seebeck coefficient (S) increases with the CIR content, with the optimal S of 120.778 ± 7.917 μVK−1 at 60 wt% which exceeds that of PP by a factor of ∼ 6. The highest power factor (PF) has been found to be 81.663 ± 2.346 μWm−1K−2 at 60 wt% which is 6 times larger than that of PP. The thermal conductivity k increases to be 0.680 ± 0.017 Wm−1K−1 at 70 wt%. The films exhibit a maximum zT of 0.039 ± 0.003 for 60 wt% at room temperature which is greater than that of PP by 2.7 times. This study offers simple, safe, economic, and effective TE composites with a large Seebeck coefficient which can be actually applied in TE generators and temperature sensors.

Tuning of band gap by anions (Cl, Br, I) of double perovskites Rb2AgAsX6 (Cl, Br, I) for solar cells and thermoelectric applications

The high stability, lead free, environment friendly and excellent performance of double perovskites make them emerging materials for solar cells and thermoelectric generators. Therefore, here optical, electronic, and thermoelectric characteristics of Rb2AgAsX6 (X = Cl, Br, I) are studied comprehensively by first principle approach. The thermodynamic stability is ensured through formation energy and structural stability by calculating tolerance factor. The studied DPs band gaps are tuned from 2.21 eV to 1.50 eV, and 0.52 eV by the replacing the anions (Cl to Br, and I). The absorption regions from varies from infrared to visible regions which increase their significance for diverse applications in optoelectronics. The broad absorption band of Rb2AgAsI6 in visible region is important for solar cells. Furthermore, the thermoelectric performance has been elaborated by power factor and figure of merit. The ultralow lattice thermal conductivity, and large Seebeck coefficient also increase the figure of merit to realize them for thermoelectric applications.

Room‐Temperature Self‐Powered Terahertz Photodetection in Ge‐Intercalated Topological Insulator GeBi4Te7

Topological insulators (TIs) are under rapid and intensive study in the fields of condensed matter physics, due to exotic electronic properties. Recent studies of photocurrent generation in topological surface states (TSS) properties have insufficient evidence to rule out that of bulk states, hindering the application in optoelectronics. Herein, the chemical vapor transport (CVT) synthesis of GeBi4Te7 crystal by the way of Ge intercalation is realized, enabling isolated Dirac points‐associated high‐mobility Dirac carriers and larger Seebeck coefficients. Then, the antenna‐coupled photodetector in GeBi4Te7 based on planar metal–TI–metal structure is reported, successfully realizing sensitive terahertz response without bias. According to the results, the GeBi4Te7‐based terahertz photodetector has a short response time and a high photoresponsivity (0.42 A W−1 at 0.107 THz and 0.6 A W−1 at 0.28 THz, respectively). The GeBi4Te7–graphene heterostructure can further improve the responsivity by more than two orders of magnitude, reaching 12 A W−1 at 0.107 THz. These findings bring up doable avenues for GeBi4Te7 materials’ low‐energy optoelectronic applications.

Thermoelectric properties and lattice dynamics of tetragonal topological semimetal Ba3Si4.

We report the lattice dynamics and thermoelectric properties of topological semimetal Ba3Si4. The lattice dynamics has been studied by Raman and inelastic neutron scattering experiments. Good agreement has been found with first-principles calculations. The presence of low-energy optical modes at about 7 meV mainly due to the heavy mass of the Ba atoms suggests a propensity to low thermal conductivity, which is favorable for thermoelectric applications. Our density functional theory calculations indicate that the semimetallic nature of Ba3Si4 is the origin for the rather large thermopower. Ba3Si4 shows high potential for a thermoelectric material with a Seebeck coefficient as large as -120 μV K-1 for 0.2 electrons/formula units through the substitution of Ba by appropriate cations, such as Y.

Anisotropic ductility and thermoelectricity of van der Waals GeAs.

Wearable thermoelectric applications require materials with both high energy conversion efficiency and excellent flexibility/deformability. Inorganic thermoelectric materials have shown high conversion efficiency, but they are usually brittle and have poor mechanical flexibility, which makes their integration into flexible devices a challenging task. GeAs is a group IV-V binary compound with a van der Waals layered structure, and its thermoelectric response has been reported. Herein, we investigate the mechanical and thermoelectric properties of GeAs crystal by a combination of density functional theory and density functional perturbation theory methods. Our results show that GeAs features a moderately dispersive valence band and multivalley convergence, which give rise to a large Seebeck coefficient and power factor when it is properly p-doped. Remarkably, its electrical transport in the out-of-plane direction even outperforms that in the in-plane direction, while phonon transport is suppressed, leading to a predominant thermoelectric response in the vertical direction. More interestingly, GeAs demonstrates a structural stiffness higher than thermoelectric CuInTe2 and PbTe, and a ductility ratio comparable to a recently discovered plastic semiconductor, InSe. The stress-strain curve simulation reveals that GeAs can withstand deformations up to 20%. These findings showcase GeAs as a ductile thermoelectric material suitable for wearable devices and energy conversion.

Enhanced Density of States Facilitates High Thermoelectric Performance in Solution-Grown Ge- and In-Codoped SnSe Nanoplates

SnSe single crystals have gained great interest due to their excellent thermoelectric performance. However, polycrystalline SnSe is greatly desired due to facile processing, machinability, and scale-up application. Here, we report an outstanding high average ZT of 0.88 as well as a high peak ZT of 1.92 in solution-processed SnSe nanoplates. Nanosized boundaries formed by nanoplates and lattice strain created by lattice dislocations and stacking faults effectively scatter heat-carrying phonons, resulting in an ultralow lattice thermal conductivity of 0.19 W m-1 K-1 at 873 K. Ultraviolet photoelectron spectroscopy reveals that Ge and In incorporation produces an enhanced density of states in the electronic structure of SnSe, resulting in a large Seebeck coefficient. Ge and In codoping not only optimizes the Seebeck coefficient but also substantially increases the carrier concentration and electrical conductivity, helping to maintain a high power factor over a wide temperature range. Benefiting from an enhanced power factor and markedly reduced lattice thermal conductivity, high average ZT and peak ZT are achieved in Ge- and In-codoped SnSe nanoplates. This work achieves an ultrahigh average ZT of 0.88 in polycrystalline SnSe by adopting nontoxic element doping, potentially expanding its usefulness for various thermoelectric generator applications.

Tuning of band gap by anion variation of double perovskites K2AgInX6 (X = Cl, Br) for solar cells and thermoelectric applications

In recent research double perovskites have become the burning topic for solar cells because of lead free nature, stability, and exceptional performance. Therefore, here we have explained the optical and transport properties of K2AgInX6 (X ​= ​Cl, Br) for solar cells and thermoelectric generators. The confirmation of thermodynamic stability been reported by formation energy and structural existence by tolerance factor. The band gaps of 2.34 ​eV, 1.37 ​eV, and 0.0 ​eV are computed from the band structures for K2AgInCl6, K2AgInBr6, and K2AgInI6, respectively. The band gap of K2AgInBr6 is found ideal for solar cells having large absorption band (376–612 ​nm) in the visible region. The optical characteristics of K2AgInCl6, and K2AgInBr6 are argued in terms of dielectric constants, refractive index, optical loss, and reflection of light. Finally, the thermoelectric behavior has been described by power factor and figure of merit in terms of carrier's concentration and temperature. The large Seebeck coefficient and remarkably small lattice conductivity increases their significance for thermoelectric generators.

Thermal Transport and Thermoelectric Properties of Rb2PdX6 (X=Cl, Br) from First‐principles Study

AbstractVacancy‐ordered double perovskites are characterized by stable structure, non‐toxicity, low thermal conductivity, and large Seebeck coefficient, which are potential thermoelectric materials. In this work, the thermal transport and thermoelectric properties of Rb2PdX6(X=Cl, Br) are theoretically investigated. We find that the calculated thermal conductivity is underestimated from the phonon Boltzmann transport equation (PBTE) since the mean free path of a large number of phonons is less than the Ioffe‐Regel limit. The room‐temperature thermal conductivities of Rb2PdCl6 and Rb2PdBr6 are 0.42 W m−1 K−1 and 0.22 W m−1 K−1 based on two‐channel phonon transport mode, respectively. The thermal conductivity of Rb2PdBr6 is almost unchanged with the temperature. Rb2PdX6(X=Cl, Br) have large Seebeck coefficient for p‐type doping due to triple degeneracy in the VBM and the thermoelectric property of p‐type doping is better than that for n‐type doping. The ab initio scattering and transport program (AMSET) is used to calculate the electron scattering rate. At 700 K, the maximum ZT of p‐type doping Rb2PdCl6 and Rb2PdBr6 can reach to 0.51 and 1.31, respectively. Replacement of Cl by Br results in lower thermal conductivity and smaller bandgap, and thus larger the maximum ZT value. This work demonstrates that Rb2PdBr6 is a potential high‐performance p‐type thermoelectric perovskite material.

Comparison of thermoelectric properties of sorted and unsorted semiconducting single-walled carbon nanotube free-standing sheets

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are promising materials for thermoelectric generation (TEG) because of their large theoretical Seebeck coefficient (S). In this study, to discuss superiority of s-SWCNTs for TEG devices, thermoelectric properties of free-standing s-SWCNT sheets were compared with unsorted SWCNT sheets. To obtain the highest power density, the films were doped with triethyloxonium hexachloroantimonate and 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzo[d]imidazole as the hole and electron dopants, respectively. The doped s-SWCNT sheets exhibited higher S but lower electrical conductivity than those of the unsorted SWCNT sheets. Consequently, the power factor of the s-SWCNT sheets was lower than that of the unsorted SWCNT sheets.

Lattice Distortions and Multiple Valence Band Convergence Contributing to High Thermoelectric Performance in MnTe.

Here, a new route is proposed for the minimization of lattice thermal conductivity in MnTe through considerable increasing phonon scattering by introducing dense lattice distortions. Dense lattice distortions can be induced by Cu and Ag dopants possessing large differences in atom radius with host elements, which causes strong phonon scattering and results in extremely low lattice thermal conductivity. Density functional theory (DFT) calculations reveal that Cu and Ag codoping enables multiple valence band convergence and produces a high density of state values in the electronic structure of MnTe, contributing to the large Seebeck coefficient. Cu and Ag codoping not only optimizes the Seebeck coefficient but also substantially increases the carrier concentration and electrical conductivity, resulting in the significant enhancement of power factor. The maximum power factor reaches 11.36 µW cm-1 K-2 in Mn0.98 Cu0.04 Ag0.04 Te. Consequently, an outstanding ZT of 1.3 is achieved for Mn0.98 Cu0.04 Ag0.04 Te by these synergistic effects. This study provides guidelines for developing high-performance thermoelectric materials through the rational design of effective dopants.

The atomic layer thermopile heat flux sensor based on the inclined epitaxial YBa2Cu3O7-δ films

The atomic layer thermopile (ALTP) heat flux sensor based on highly c-axis oriented YBa2Cu3O7-δ (YBCO) films prepared on miscut 12° LaAlO3 substrates using magnetron sputtering is achieved. Benefiting from good biaxial texture, the YBCO film maintains a large Seebeck coefficient anisotropy, so the sensitivity of the ALTP heat flux sensor reaches 17.54 μV/(kW/m2). In addition, the response frequency of the sensor is higher than 1 MHz due to the high electrical conductivity of the prepared YBCO films, which is also higher than the current maximum (650 kHz) reported in the literature. These results indicate that our ALTP heat flux sensor can realize high-frequency heat flux detection above 1 MHz.

Enhancement of the anomalous Nernst effect in epitaxial Fe4N films grown on SrTiO3(001) substrates with oxygen deficient layers

Anomalous Nernst effect of epitaxial Fe4N films on MgO(001), MgAl2O4(MAO)(001), and SrTiO3(STO)(001) substrates grown by molecular beam epitaxy was investigated. Moderately large anomalous Nernst coefficients (SANE) of 1.4 and 1.7 μV/K were obtained in the Fe4N films on the MgO(001) and MAO(001) substrates, respectively, and large anomalous Hall angles (∼0.06) and transverse thermoelectric conductivities [∼1.3 A/(m K)] were derived from the experimental results. On the other hand, a large effective SANE of 2.8 μV/K was obtained in the Fe4N film on the STO(001) substrate. The origin of the enhanced effective SANE is the negatively large Seebeck coefficient (SSE) in an oxygen deficient STO layer near the surface of the STO substrate. This indicates that it is possible to enhance the effective SANE of ferromagnetic materials by utilizing adjacent materials with large |SSE| such as the oxygen deficient STO layer.