Higher Power Factor Values Research Articles

Improving the thermoelectric performance of hydrothermally synthesized FeS2 nanoparticles by post sulfurization

In this manuscript, we have synthesized the FeS2 nanoparticles by a simple hydrothermal method. Post sulfurization of the synthesized nanoparticles for different time durations (30, 60, 90 & 120 min) was performed to obtain quality samples. XRD data exhibits the phase development of FeS2 particles while some secondary phases related to FeS were also observed. Raman spectroscopy data confirm the formation of pyrite FeS2. Seebeck data suggested an improvement in Seebeck coefficient value from 44 to 88 μV/°C as the sulfurization duration was increased from 30 to 120 min. A similar increasing trend was also observed for the electrical conductivity values. This kind of improvement in the Seebeck coefficient and electrical conductivity was related to the improvement in the FeS2 pyrite phase. This improvement in crystal structure resulted in the improvement of the mobility of the carriers which leads to a high power factor value up to 3.8 × 10−5Wm−1K−2.

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.

Thermal Treatment Effects on the Thermoelectric Properties of Ni/Si/Si + Sb/Si/Si + Ge/Ni Multilayer Thin Films

The multilayer thermoelectric devices including Ni/200 layers of Si/Si + Sb/200 layers of Si/Si + Ge/Ni thin films were fabricated using electron beam and DC/RF magnetron sputtering deposition systems. The thickness measurements have been performed using Filmetrics UV thickness measurement system. The Au contacts at the bottom and top of the fabricated thermoelectric devices were measured as 100 nm for each side. Ni layer at the bottom is 108 nm and Ni layer at the top of the multilayer structures is 168 nm. The thickness of 200 layers of Si/Si + Ge thin film is 173 nm and the thickness of 200 layers of Si/Si + Sb thin film is 199 nm. The fabricated thermoelectric devices have total of 402 layers of thin films with the total thickness of 648 nm thickness excluding two Au contact layers. The prepared thin film devices were annealed at different temperatures for one hour to improve the thermoelectric properties. The current studied system has reached some remarkable values of Seebeck coefficients when the suitable annealing temperatures and the suitable operating temperatures of Seebeck measurement system were applied. The multilayer thin film system has reached the Seebeck coefficient of -344.8 μV/K when the annealed temperature was 100°C and the operating temperature was 320 K. One of the main problems with the thermoelectric devices is having higher temperature dissipation during the operation of the devices. Ni thin film was used in the fabrication process to remove excess of the heat as a heat sink from the thermoelectric devices. This will bring new approach for the high efficient thermoelectric devices. The goal of the manuscript is to improve the thermoelectric properties of the fabricated thin film thermoelectric devices using Ni thin films and the thermal treatment. The resistivity values decreased when the annealing temperatures increased. The highest power factor values were reached when the thermoelectric devices were annealed at 100°C. Mobility values increased when the suitable temperatures were applied for thermal treatment.

Improved thermoelectric performance of Al and Sn doped ZnO nano particles by the engineering of secondary phases

Controlling the generation of secondary phases is crucial to enhance the thermoelectric performance of any material. In this manuscript, we have demonstrated the modulation of thermoelectric properties of Al and Sn doped ZnO nano particles by the post annealing method. Al doped ZnO (ZAO) and Sn doped ZnO (ZTO) nano particles were synthesized by the simple hydrothermal technique. After growth, both samples were annealed at 800 °C for 1 h. The Seebeck data suggested that the annealed ZTO sample has the highest value of Seebeck coefficient as compared to its counterpart as grown and ZAO samples as well. This highest value of Seebeck coefficient is related to generation of secondary phases in annealed ZTO. The generation of secondary phases was also causing an enhancement in mobility of the carriers. This carriers, mobility enhancement resulted in the high electrical conductivity value for ZTO sample leads to the highest value of power factor for ZTO about 1.2 × 10-4 Wm-1K-2. The XRD data confirmed that ZAO samples have better crystal quality as compared to ZAO samples. The poor crystal quality of ZTO is due the presence of SnO based secondary phases. For further verification of this argument, we have performed Raman spectroscopy and SEM measurements which supported our proposed argument.

Exploration of uranium double perovskites Ba2MUO6 (M = Co, Ni) for magnetism, spintronic and thermoelectric applications

Ba2MUO6 (M = Co, Ni) alloys are investigated to understand their electronic structure, magnetic character together with thermoelectric behavior using ab-initio formulism. The variations in physical properties by changing M-site atom are analyzed. The crystal structure of Ba2MUO6 (M = Co, Ni) alloys is found to be face-centered cubic (Fm-3m) with lattice constant of 0.845 nm for Ba2CoUO6 and 0.841 nm for Ba2NiUO6. The band structure and density of states convey half-metallic ferromagnetic character of Ba2CoUO6, while Ba2NiUO6 exhibit ferromagnetic semiconducting nature. The electron filling in the d-orbitals of Co and Ni determines the overall electronic and magnetic character of alloys. The obtained structural parameters and magnetic moment are consistent with experimental results. The variation in various thermoelectric parameters with temperature is also examined. The highest value of power factor obtained for Ba2NiUO6 and Ba2CoUO6 is 54.92 μW cm−1 K−2 and 9.25 μW cm−1 K−2, respectively. The semiconducting nature in both spin orientations favors Ba2NiUO6 for thermoelectric applications. The computed elastic constants along with other elastic parameters suggest that these alloys are mechanically stable and possess ductile character.

Synergistically improving the thermoelectric performance of In2O3 via a dual-doping and nanostructuring approach

Co-substitution along with nanostructuring is typically employed to optimize thermoelectric transport properties for the development of highly efficient n-type thermoelectric materials. However, an understanding of defect chemistry plays a vital role in choosing the right substituent for the matrix of the parent structure. We investigate the thermoelectric performance of In2O3 via dual doping with Zn and Ge co-substitution. A single-phase structure with nanosized grains has successfully been obtained with Zn and Ge co-substitution even at an 8% doping concentration, using high energy planetary ball milling followed by spark plasma sintering (SPS). Zn and Ge co-doping substantially improved electrical transport by enhancing carrier concentration, which resulted in an increased effective mass with modest carrier mobility achieved sufficiently high power factor value of 9.39 μW cm−1 K−2 at 973 K observed for an 8% doping concentration. Furthermore, reduction of lattice thermal conductivity is observed from the co-substitution because of mass fluctuation scattering of the phonons. The combined effect of dual doping, the selection of the right substituent and phase purity results in an improved figure of merit ZT value of 0.36 at 973 K. This study suggests that In2O3 can be a potential material for thermoelectric applications.

High-Performance N-Type Carbon Nanotube Composites: Improved Power Factor by Optimizing the Acridine Scaffold and Tailoring the Side Chains.

Single-walled carbon nanotubes (SWCNTs)/organic small molecules (OSMs) are promising candidates for application in thermoelectric (TE) modules; however, the development of n-type SWCNT/OSMs with high performance is lagging behind. Only a few structure-activity relationships of OSMs on SWCNT composites have been reported. Recently, we find that the n-type acridone/SWCNT composites display high power factor (PF) values at high temperature but suffer from low PFs at room temperature. Here, the performance of SWCNT composites containing an acridine derivative (AD) as well as its analogues with different counterions (Cl-, SO42- and F-) and lengths of alkyl chains (ADLA1-2 and ADLA4-5) is reported. Among the composites, SWCNT/ADLA4 with no counterions exhibits the highest PF value of 195.2 μW m-1 K-2 at room temperature, which is 4.9 times higher than that of SWCNT/ADTAd (39.8 μW m-1 K-2), indicating that the acridine scaffold and the lengths of alkyl chains contribute to the dramatic changes in the TE performance. In addition, SWCNT/ADLA4 exhibits high PF values at all the temperatures we investigate, which range from 154.7 to 230.7 μW m-1 K-2. Furthermore, a TE device consisting of five pairs of p (the pristine SWCNTs)-n (SWCNT/ADLA4) junctions is assembled, generating a relatively high open-circuit voltage (41.7 mV) and an output power of 1.88 μW at a temperature difference of 74.8 K. Our results suggest that structural modifications might be an effective way to advance the development of TE materials.

Modulation of thermoelectric properties of Mg2GeO4 thin films by controlling the growth process

Abstract The aim of present study is to enhance the thermoelectric properties of Mg2GeO4 thin films via controlling the growth mechanism by varying the source-substrate distance during the thermal evaporation process in tube furnace. The samples were grown using fixed pressure (2 × 10-3 torr), oxygen flow rate (100 sccm), evaporation temperature (950 0C) and varying source-substrate distance (5-15 cm). The XRD data demonstrated that sample grown using source-substrate distance 15 cm has best crystal structure while 5 cm sample has poor quality. The poor crystal quality is due to the presence of oxygen vacancy type defects. This dependence of crystal structure on source-substrate distance was also studied by Raman spectroscopy measurements. The Raman graph showed that sample grown using source-substrate distance 10 cm has amorphous structure because it has only Si peak at 521 cm-1. But the Raman spectra of samples grown using 5 and 15 cm distances show peaks due to Raman modes of Mg2GeO4 structure. Seebeck and Hall data suggested that Mg2GeeO4 sample grown at 10 cm distance posses high values of Seebeck coefficient, electrical conductivity and power factor with values 1998 μV/0C, 125 S/cm and 8.1 × 10-3 Wm-1K-2 respectively. These high values of thermoelectric properties are related with the higher carrier concentration of the sample grown using source-substrate distance 10 cm. This argument was further verified by Hall data which confirmed that his sample has highest electrical conductivity.

Power Converter with High Value of Power Factor

Power Converter with High Value of Power Factor

Impact of aluminum on the Seebeck coefficient and magnetic properties of La0.7Ba0.3MnO3 manganites

• Al effect on the thermopower and magnetic susceptibility of La 0.7 Ba 0.3 MnO 3 compound. • The composites are still a single phase rhombohedral despite adding Al 2 O 3 phase. • Power factor values decrease with increasing Al content. • (LaBaMnO) 0.975 /(AlO) 0.025 composite record the highest value of power factor. • TEP data satisfy the Magnon and Phonon drag model and SPH conduction mechanism. The effect of aluminum on (La 0.7 Ba 0.3 MnO 3 ) 1-x /(Al 2 O 3 ) x composites is investigated based on their crystal structure, thermoelectric power and magnetic properties. The X-ray diffraction process reveals that the composite still exhibits a rhombohedral perovskite structure R 3 ¯ C of all composites. The thermoelectric power data satisfies the Magnon and Phonon-drag models in the low-temperature range, and the smaller Polaron conduction mechanism in the high-temperature range. The power factor values decrease with Al content and the x = 0.025 record the highest value. All composites undergo ferromagnetic to paramagnetic transition at a certain temperature T C . The AC susceptibility values decrease with the increasing Al content.

Optical, Electrical, and Thermoelectric Properties of Hydrothermally Synthesized Bi2Te3 Nanoflakes

Thermoelectric power generators are promising for clean energy production through converting the waste heat to electricity in environmentally friendly ways without any noise or pollutants. This work reports a facile method to synthesize Bi2Te3 nanoflakes with an investigation of their structural, optical, and thermoelectric properties. Various techniques such as X‐ray diffraction, field emission scanning electron microscope, transmission electron microscope, and energy dispersive spectroscopy are used to characterize the synthesized compound. The results confirmed that the nanoflakes crystallize in a rhombohedral structure with an average diameter and thickness ≈31.2 and 27 nm, respectively. A narrow optical band gap of 0.43 eV is determined for the prepared nanoflakes confirming the potential of employing the nanoflakes in optoelectronic applications. The results of the thermoelectric measurements imply that the synthesized nanoflakes have high power factor values at high temperatures compared to those previously reported for the same compound by other research groups. The power factor values make the synthesized nanoflakes promising candidate for thermoelectric applications.

Boosted thermoelectric properties of molybdenum oxide thin films deposited on Si substrates

[Formula: see text] has novel peculiarities and complexities due to multiple valence states of 4d molybdenum, but high carrier density impedes its thermoelectric (TE) application. Recent investigation has demonstrated that the TE performance of transition metal oxide films can be greatly enhanced by activating a parallel conduction channel in the perovskite substrates through reversible incorporation of oxygen. In this work, we report the TE properties of [Formula: see text] thin films deposited on single crystalline Si and quartz glass substrates by magnetron sputtering. The TE power factor (PF) in the former is above 40 times bigger than that in the latter. Such a large enhancement originates mainly from the significantly enhanced Seebeck coefficient, correlated with the contribution of the Si substrate. The highest PF value 1.78 mW/(m[Formula: see text]⋅[Formula: see text]K2) at 700 K in this [Formula: see text]/Si system is comparable to the state-of-the-art in other TE thin films. Based on the preceding research, our experimental results suggest a more economic and scalable route to explore high-performance TE thin films.

Magneto-Electronic, Thermodynamic, and Thermoelectric Properties of 5f-Electron System BaBkO3

In the present work, the structural, electronic, magnetic, mechanical, thermodynamic, and thermoelectric properties of cubic perovskite BaBkO3 were investigated within the framework of density functional theory using generalized gradient approximation, onsite Coulomb interaction, and modified Becke-Johnson methods. BaBkO3 is stable in the ferromagnetic phase with a magnetic moment of 7 μB. The spin-polarized electronic band structure reveals 100% spin polarization of the material with metallic character in spin-up state and semiconducting in spin-down state. Pugh and Cauchy relation displays that the material is highly ductile. The quasi-harmonic Debye model was used to determine the thermodynamic properties of BaBkO3 under high pressure and temperature. BaBkO3 presents high value of Seebeck coefficient and power factor at room temperature with a value of 135 μVK− 1 and 1.5 × 1012μWcm− 1 K− 2 s− 1, respectively. The possession of half metallicity and high Seebeck coefficient makes BaBkO3 suitable for spintronic and thermoelectric device applications.

A Single-Stage Integrated Boost-LLC AC–DC Converter With Quasi-Constant Bus Voltage for Multichannel LED Street-Lighting Applications

Single-stage boost-LLC ac–dc converters are popularly utilized as the front-end stage of multichannel LED street-lighting drivers. Pulse frequency modulation (PFM) strategy with a duty cycle of 0.5 is commonly utilized in these ac–dc converters. However, PFM has the following drawbacks: 1) high bus voltage limits the ac input voltage range, which makes it only suitable for the input voltage range of 85~135 V and 2) the maximum bus voltage can reach up to three times of the minimum bus voltage, which increases the difficulty of the LLC design. This paper proposed a hybrid modulation strategy, which consists of a bus voltage control loop using asymmetric pulsewidth modulation and an output voltage control loop using PFM. The stable output voltage and the quasi-constant bus voltage can be simultaneously achieved. Furthermore, by increasing bus voltage ripple and employing the twin-bus configuration, the short-lifetime electrolytic capacitors are eliminated, and the efficiency of the total LED driver can be greatly improved. Therefore, universal-input operation, high efficiency, low cost, and long lifetime are the key innovations of the proposed solution. A universal-input 100-W prototype is built to demonstrate the feature of the proposed solution. The experimental results show that the converter achieves a peak efficiency of 92.5% at the input voltage of 130 V and a high power factor value of above 0.95 over the whole input voltage range. With the proposed modulation strategy, the maximum bus voltage is just 500 V under universal input voltage condition, which is greatly lower than that of the traditional PFM controlled boost-LLC converters.

Possible High Thermoelectric Power in Semiconducting Carbon Nanotubes ∼A Case Study of Doped One-Dimensional Semiconductors∼

We have theoretically investigated the thermoelectric properties of impurity-doped one-dimensional semiconductors, focusing on nitrogen-substituted (N-substituted) carbon nanotubes (CNTs), using the Kubo formula combined with a self-consistent t-matrix approximation. N-substituted CNTs exhibit extremely high thermoelectric power factor (PF) values originating from a characteristic of one-dimensional materials where decrease in the carrier density increase both the electrical conductivity and the Seebeck coefficient in the low-N regime. The chemical potential dependence of the PF values of semiconducting CNTs has also been studied as a field-effect transistor and it turns out that the PF values show a noticeable maximum in the vicinity of the band edges. This result demonstrates that “band-edge engineering” will be crucial for solid development of high-performance thermoelectric materials.

Methodology of testing and optimal setting of an asynchronous traction drive for electric vehicles

This paper presents a methodology of tests of traction asynchronous drives applied in electric vehicles. It is similar to Urban Driving Cycle ECE-15 (UDC). The objective of the research is to verify the developed methodology through tests performed on a laboratory simulator, which consists of energy-saving asynchronous motor controlled by a frequency inverter (converter). Vector Control on the drive is used for smooth speed regulation over a wide range at high values of efficiency and power factor. Contemporary measuring and control devices and special software products are used for capturing the dynamic characteristics when starting, stopping and changing the speed set point of the drive. Some of tests are presented and an experimental verification of the developed methodology is made. An optimal setting of the drive parameters can be made to minimize the electric energy consumption.

High Thermoelectric zT in n‐Type Silver Selenide films at Room Temperature

AbstractIn this work, a zT value as high as 1.2 at room temperature for n‐type Ag2Se films is reported grown by pulsed hybrid reactive magnetron sputtering (PHRMS). PHRMS is a novel technique developed in the lab that allows to grow film of selenides with different compositions in a few minutes with great quality. The improved zT value reported for room temperature results from the combination of the high power factors, similar to the best values reported for bulk Ag2Se (2440 ± 192 µW m−1 K−2), along with a reduced thermoelectric conductivity as low as 0.64 ± 0.1 W m−1 K−1. The maximum power factor for these films is of 4655 ± 407 µW m−1 K−2 at 103 °C. This material shows promise to work for room temperature applications. Obtaining high zT or, in other words, high power factor and low thermal conductivity values close to room temperature for thin films is of high importance to develop a new generation of wearable devices based on thermoelectric heat recovery.

Achieving high power factor of p-type BiSbTe thermoelectric materials via adjusting hot-pressing temperature

Achieving high power factor values for BiSbTe alloys is important for further elevation of their thermoelectric performance. In this report, Bi0.4Sb1.6Te3 bulk samples were prepared by a fusion method followed by hot pressing at different temperatures (523 K, 573 K, 623 K and 663 K), and their thermoelectric properties were investigated from 300 K to 500 K. It was found that the power factor and thermal conductivity increased significantly with increasing hot-pressing temperature. A record power factor of 53.8 μW/(cm K2) at 300 K was achieved for the sample hot pressed at 663 K. In addition, a maximum ZT of 1.3 at 413 K and average ZTave of 1.2 at 300–500 K were achieved for the sample hot pressed at 623 K.

Thermoelectric Films: Pulsed Hybrid Reactive Magnetron Sputtering for High zT Cu2Se Thermoelectric Films (Adv. Mater. Technol. 7/2017)

In article number 1700012, Marisol Martin-Gonzalez and co-workers report a novel technological approach to deposit highly efficient thermoelectric films via the pulsed hybrid reactive magnetron sputtering (PHRMS). PHRMS is a single-step fabrication process with the ability to get even at room temperature high values of power factor and low values of thermal conductivity for films with the β-Cu2Se phase and transferable to industry even for 2D materials.

Preparation of high performance Bi2Sr2Co1.8Ox thermoelectric materials from nanosized precursors

ABSTRACTBi2Sr2Co1.8Ox thermoelectric (TE) materials were prepared by three different synthesis methods producing nanosized precursors: coprecipitation (with ammonium carbonate or oxalic acid) and attrition milling, which were compared with those obtained by the classical solid state method. Microstructure has shown that precursors produced by coprecipitation and attrition milling methods produced nanometric precursors much smaller than the typical sizes produced by the solid state route. The TE properties are in agreement with the microstructural features, leading to lower resistivity in all the samples, compared with the solid state ones, while Seebeck coefficient is practically unchanged in all cases. As a consequence, maximum power factor values of around four times higher than those obtained in the classical solid state method have been determined. Moreover, the highest power factor value at 650°C is higher than the best results obtained in as-grown textured materials produced by the laser floating zone technique.