Improvement Of Seebeck Coefficient Research Articles

Nanoconfinement Effect in Water Processable Discrete Molecular Complex-Based Hybrid Piezo- and Thermo-Electric Nanogenerator.

Water-processable hybrid piezo- and thermo-electric materials have an increasing range of applications. We use the nanoconfinement effect of ferroelectric discrete molecular complex [Cu(l-phe)(bpy)(H2O)]PF6·H2O (1) in a nonpolar polymer 1D-nanofiber to envision the high-performance flexible hybrid piezo- and thermo-electric nanogenerator (TEG). The 1D-nanoconfined crystallization of 1 enhances piezoelectric throughput with a high degree of mechano-sensitivity, i.e., 710 mV/N up to 3 N of applied force with 10,000 cycles of unaffected mechanical endurance. Thermoelectric properties analysis shows a noticeable improvement in Seebeck coefficient (∼4 fold) and power factor (∼6 fold) as compared to its film counterpart, which is attributed to the enhanced density of states near the Fermi edges as evidenced by ultraviolet photoelectric spectroscopy and density functional based theoretical calculations. We report an aqueous processable hybrid TEG that provides an impressive magnitude of Seebeck coefficient (∼793 μV/K) and power factor (∼35 mWm-1K-2) in comparison to a similar class of materials.

Investigating the thermoelectric power generation performance of ZnCuO: A p-type mixed-metal oxide system

Thermoelectric power generation performance of ZnCuO nanostructures is enhanced by varying the concentration of Cu atoms. This is tested by growing samples of ZnCuO by simple hydrothermal route at different Cu concentrations (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5). The X-ray diffraction (XRD) pattern shows the formation of mixed-metal oxide phases of ZnO and CuO, while the increase in Cu concentration results in generation of more stable CuO phases. Raman spectroscopy measurement is performed for all synthesized samples, which supports the XRD results. For the thermoelectric and electric conductivity behavior, Seebeck coefficient and Hall measurements are performed for all samples. Data suggest an improvement in Seebeck coefficient from 32 to 73 μV°C−1 with the increase of Cu concentration in the host crystal. Electrical conductivity data also show a similar increasing trend (19–36 Scm−1) resulting in a high power-factor value of 1.12 × 10−5 Wm−1K−2 for the sample with highest Cu concentration. This enhanced thermoelectric performance with increasing concentration of Cu atoms is due to the improvement of carrier mobility. The mobility of carriers is thought to increase because of the emergence of mixed composite phases, as verified by XRD and Raman spectroscopy measurements.

Mechanical alloying boosted SnTe thermoelectrics

The well converged transporting valence bands in SnTe-MnTe alloys ensures a superior electronic performance, while their thermal transport properties still need to be further optimized for higher thermoelectric performance. Herein, the mechanical alloying is utilized to fabricate the SnTe-15%MnTe-2%Bi alloys, leading to a remarkable reduction of grain size as well as the formation of dense dislocations. Unexpectedly, the solubility of MnTe is reduced to ∼6% by mechanical alloying at room temperature, inducing an enhanced phonon scattering from nanoprecipitates. These full-scale hierarchical microstructures effectively decrease the lattice thermal conductivity of SnTe-15%MnTe-2%Bi to ∼0.5 W m−1 K−1 at 850 K. In addition, the increased vacancy formation energy triggers a reduction in carrier concentration (∼3 × 1019 cm−3) due to the decreased MnTe content in matrix. Moreover, the energy filtering effect through precipitate-matrix interface enables an improvement in Seebeck coefficient. Accordingly, the figure of merit of SnTe-15%MnTe-2%Bi is dramatically increased to ∼1.5 at 850 K by mechanical alloying. This work clearly demonstrates that mechanical alloying changes the composition and microstructure of materials, which significantly affect the thermoelectric transport properties, enabling an obvious performance enhancement.

Modulation of thermoelectric properties of thermally evaporated copper nitride thin films by optimizing the growth parameters

In this paper, we have successfully controlled the thermoelectric properties of copper nitride (Cu3N) thin films by optimizing the post growth nitrogen gas flow time. During thermal evaporation growth of Cu3N thin films, pure copper power (0.12 g) was evaporated on soda lime glass substrate. The boat temperature and nitrogen gas flow rate were fixed at 1010 °C and 100 sccm respectively in horizontal glass tube furnace. In order to study the annealing time duration, all samples were annealed at 320 °C in tube furnace for 2–8 h with constant flow rate of 100 sccm. The formation of Cu3N phase was confirmed by X-Ray Diffraction (XRD) and it was found that crystallinity of grown thin films was improved with annealing time duration. The Seebeck data demonstrated that the value of Seebeck coefficient was increased form 87.59 μV/°C to 134.79 μV/°C as the annealing time duration was increased from 2 to 8 h. This improvement in Seebeck coefficient was associated with the enhancement of samples crystallinity which ultimately increase the mobility of charge carriers. The value of electrical conductivity was also increased from 26.04 S/cm to 33.49 S/cm, therefore we were able to achieve the highest value of power factor (6.08 × 10−5 Wm−1C−2) for sample annealed for maximum time duration. Raman spectroscopy and SEM measurements were additionally performed to strengthen our proposed argument.

Effects of inorganic salt NaNbO3 composite on the thermoelectric properties of tellurium nanorods thin slice

There has recently been increased interest in tellurium nanomaterials (Te NMs)-based thermoelectric (TE) materials owing to their large Seebeck coefficient. Meanwhile, techniques such as doping, alloying, and composite have been intensively investigated to further enhance the TE performance of Te NMs-based energy conversion devices. However, the effects of certain inorganic salts on the TE performance of Te NMs have not been studied thus far. Herein, an inorganic salt NaNbO3 was employed to prepared the Te nanorods (Te-NRs) composite as TE material via a hydrothermal method. Furthermore, the chemical composition, microstructure, thermal stability, and TE performance were systematically investigated for NaNbO3/Te-NRs composites at room temperature. By optimization, the NaNbO3/Te-NRs composite with the mass ratio of 1:1 achieved a simultaneous improvement in Seebeck coefficient and electrical conductivity resulting a large TE power factor (PF) of 43.5 μW m−1 K−2 and a high figure of merit (ZT) of 0.081 which are 8 times higher than the pure Te-NRs. In addition, the introduction of NaNbO3 effectively improves the environmental stability of Te-NRs due to the formation of interfaces between NaNbO3 and Te-NRs. This composite strategy proposed a novel approach to develop a promising TE material.

Uniaxial Tensile Strain Induced the Enhancement of Thermoelectric Properties in n-Type BiCuOCh (Ch = Se, S): A First Principles Study.

It is well known that the performance of thermoelectric measured by figure of merit ZT linearly depends on electrical conductivity, while it is quadratic related to the Seebeck coefficient, and the improvement of Seebeck coefficient may reduce electrical conductivity. As a promising thermoelectric material, BiCuOCh (Ch = Se, S) possesses intrinsically low thermal conductivity, and comparing with its p-type counterpart, n-type BiCuOCh has superior electrical conductivity. Thus, a strategy for increasing Seebeck coefficient while almost maintaining electrical conductivity for enhancing thermoelectric properties of n-type BiCuOCh is highly desired. In this work, the effects of uniaxial tensile strain on the electronic structures and thermoelectric properties of n-type BiCuOCh are examined by using first-principles calculations combined with semiclassical Boltzmann transport theory. The results indicate that the Seebeck coefficient can be enhanced under uniaxial tensile strain, and the reduction of electrical conductivity is negligible. The enhancement is attributed to the increase in the slope of total density of states and the effective mass of electron, accompanied with the conduction band near Fermi level flatter along the Γ to Z direction under strain. Comparing with the unstrained counterpart, the power factor can be improved by 54% for n-type BiCuOSe, and 74% for n-type BiCuOS under a strain of 6% at 800 K with electron concentration 3 × 1020 cm−3. Furthermore, the optimal carrier concentrations at different strains are determined. These insights point to an alternative strategy for superior thermoelectric properties.

Enhanced thermoelectric properties of Ca3Co4O9+δ ceramics by Sr substitution

Ca3-xSrxCo4O9+δ (CCO-Srx) with varying strontium (Sr) content (x = 0.4, 0.5, 0.6, and 0.7) were synthesized by solid-state method. The crystal structures and morphologies of Ca3-xSrxCo4O9+δ thermoelectric ceramics were analyzed by XRD and SEM. Micro structural characterizations have shown that all samples are composed by the same oriented plate-like grains with similar sizes about 1–3 μm diameters and 0.2–0.5 μm thicknesses. The results of XRD have shown that no secondary phases have been produced, which indicated that Sr has been incorporated into the Ca3Co4O9 phase. The diffraction peak (00l) shifted to a lower angle and the offset is increasing with the increase of Sr content, which indicated that the Sr cations can enter the Ca-sites of the Ca3-xSrxCo4O9+δ, and cause increase of the length of the C axis. Slight improvements in the Seebeck coefficient (S) and electrical resistivity (ρ) were observed across all Sr-substitution samples when the mol% of Sr was adjusted. The improvement in both electrical resistivity and Seebeck coefficient leads to higher power factor (PF) values for the ceramics. The measured results show that the highest power factor value around 0.21 mW m−1K−2 can be obtained in Ca2.4Sr0.6Co4O9+δ at 650 °C, which is 16.7% higher than the undoped sample, The ZT value of 0.37 at 650°Cfor the CCO–Sr0.6 sample is significantly higher than that of the pure CCO sample. The results show that Sr can be as an effective doping element to reduce the thermal conductivity and enhance the Seebeck coefficient for the CCO system. It can be concluded that x = 0.6 is the optimal Sr for Ca substitution in this material system.

Enhanced thermoelectric performance of n-type PbTe through the introduction of low-dimensional C60 nanodots

Lead telluride (PbTe) has long been considered as an ideal p-type thermoelectric material at an intermediate temperature range. However, the relatively low thermoelectric performance of n-type PbTe largely limits the commercial applications of integral PbTe devices. In current work, we report that a significant enhancement of the ZT value of ≈1.3 can be achieved at 823 K in PbTe0.998I0.002-0.5%C60 by adding low-dimensional C60 nanodots. This remarkable improvement in thermoelectric performance is attributed to the incorporation of C60 in n-type PbTe matrix, which creates dense nanodots that can simultaneously manipulate electron and phonon transport. On one hand, the dispersion of C60 nanodots in n-type PbTe matrix leads to highly depressed lattice thermal conductivity (κlat) (∼52%) due to the refinement of grains and the extra phonon scattering centers. On the other hand, the introduction of C60 nanodots increases the scattering parameter rx, and brings about the overall improvement of Seebeck coefficient S, especially at room temperature. This work demonstrates the great potential of low-dimensional dopant in optimizing PbTe thermoelectric materials, which should be equally applicable in improving the performance of other thermoelectric materials.

Improving the thermoelectric properties of carbon nanotubes through introducing graphene nanosprings

Carbon nanotube (CNT) is a typical one-dimensional nanomaterial containing sp2 hybridization states. In this paper, we investigate the ballistic thermoelectric performance of CNTs incorporating graphene nanosprings by using non-equilibrium Green's function. The calculations reveal that the thermoelectric figure of merit could be obviously improved by introducing graphene nanosprings, which is about ten times of that of pristine CNTs at 700 K. Such enhancement is mainly attributed to the remarkable suppression of phononic and electronic thermal conductance and improvement of Seebeck coefficient. In addition, compared to the zigzag graphene nanospring, introducing of the armchair case possesses better thermoelectric performance. The results presented in this paper indicate that embedding graphene nanospring is a viable method to optimize the thermoelectric performance of CNTs and could provide useful theoretical guidance for design and fabrication of CNTs-based thermoelectric devices.

Improvement of Seebeck coefficient in as-grown Bi2Te3-ySey electrodeposited films by the addition of additives and bath optimization

Bi2.0Te2.7Se0.3 is the most widely used thermoelectric n-type leg for large-scale cooling applications. However, as-grown electrodeposited Bi2Te3-ySey films typically have a Seebeck coefficient around a third of the bulk value, which sometimes can be improved with thermal annealings. In this work, we report as-grown Bi2Te3-ySey films having a Seebeck coefficient of approximately half the value of bulk without additional thermal treatments. All samples reported were deposited in baths containing no additives, sodium lignosulfonate (SLS), or both SLS plus ethylenediaminetetraacetic acid (EDTA) with a concentration of 1 M HNO3 (pH of 0 ± 0.1) and 0.6 M HNO3 (pH of 0.3 ± 0.1). For each scenario, the deposition was carried out at two different temperatures (0 °C and 5 °C). Seebeck values of −120 μV K−1 have been measured for as-grown films with an optimum morphology and stoichiometry (Bi2Te2.7Se0.3), which is ∼50% of the value obtained for this composition in bulk and the highest among as-grown electrochemically deposited films reported to date. These results are an incentive to revisit and further explore the chemistry behind the electrodeposition of bismuth telluride selenide films to improve the performance of electrodeposited thermoelectric films.

Effect of Annealing on Virgin and Recycled Carbon Fibre Electrochemically-deposited with N-type Bismuth Telluride

N-type thermoelectric bismuth telluride (Bi2Te3) was deposited on virgin carbon fibre (VCF) and recycled carbon fibre (RCF) substrates by electro-deposition. The effects of annealing on the surface morphology and the Seebeck coefficient of the Bi2Te3 films were investigated. A nearly stoichiometric N-type Bi2Te3 was obtained from an electrolyte of 8 mM of Bi(NO3)3.5H2O and 10mM of TeO2, which exhibited the highest Seebeck coefficient of -20.1 µV/K and -13.0 µV/K for VCF and RCF individually. The effect of varying annealing temperature (548.15 K and 623.15 K) and annealing time (2 and 3 h) was carried out only on nearly stoichiometric N-type Bi2Te3 that revealed improvement in Seebeck coefficient up to 1.51 times and 1.24 times for VCF and RCF at 623.15 K for 2 h.

Approaches to thermal isolation with thin-film superlattice thermoelectric materials

ABSTRACTWe propose the use of hetero-structured high ZT materials in thermally isolated thermoelectric couples for the purpose of improving overall device efficiency. Use of high ZT material incorporated in convective flow devices will yield a two-fold improvement in COP over isothermal TE devices. The analytical approach presented in this paper requires optimization of TE element aspect ratio according to available ΔT at location in the device. We discuss the limitations on thermoelectric element characteristics and geometry to achieve high COP. We also utilize moderate temperature differentials to meet the target of high COP. If space requirements are restrictive, or materials processing is limited, the materials described herein provide the unique ability to alter Seebeck coefficient, thermal conductivity, and electrical such that the required aspect ratio is suitable. Improvement in Seebeck coefficient and electrical resistivity independently increase COP by as much as 25% or more when applied to thermally isolated device considered.