Higher Power Factor Values Research Articles

Power control of electric heating elements using thyristor voltage and resistance converters

This article investigates the energy efficiency of thyristor converters with an active load. The conversion of electric energy in a “thyristor converter – electric heating element” installation is considered from the standpoint of electromagnetic theory. The energy characteristics of the considered installation was calculated in the MATLAB environment. When thyristor voltage converters are operated under the mode of controlling the power of active load, passive power was found to be generated at the input during the non-conductive state of the converter (thyristor is locked). The use of passive power allows additional thermal energy to be obtained by means of an extensive use of voltage, without increasing the current consumption. An increase in the depth of power control of electric heating elements by thyristor voltage converters leads to a significant increase in passive power. In the active power control range (50–100% of the nominal value), the factor accounting for variations in the total power in the converter due to an incomplete use of the voltage at the input of the considered installation decreases from 1.0 to 0.93. This reduces the power factor of the load converter from 0.97 to 0.925. Despite the high value of the load power factor (in the control interval 0–50% of the rated power value), the factor accounting for variations in the total power was found to be reduced to 0.66. As a result, the power factor of the converter with the load is reduced by ~ 33%. In order to increase the efficiency of converting electrical energy to control the active load power, it is proposed to use thyristor resistance converters that vary the electrical resistance of the load over time. It is shown that unsatisfactory operation of a thyristor voltage converter can be caused by inefficient use of voltage at the input of the “thyristor converter – electric heating element” installation. When using thyristor resistance converters, the current non-sinusoidality factor does not exceed 1.5 % and the voltage non-sinusoidality factor in a 0.38 kV network does not exceed 0.2 %.

Study of Structural, Electronic and Thermoelectric Properties of ZrP2 monolayer

The structural, electronic and thermoelectric properties of ZrP2 monolayer is studied using density functional theory and Boltzmann transport theory. The electronic band structure calculations demonstrate that this monolayer is a direct band gap semiconductor (Eg= 0.78 eV). The ZrP2 monolayer has hexagonal lattice structure, having a lattice constant 3.04 Å. The energetic, mechanical and dynamic stability of the ZrP2 monolayer is checked and it is found to be stable. The transport coefficients are calculated using Boltztrap code. The lattice thermal conductivity is calculated using Slack’s equation and found to be very low at room temperature. High value of power factor and low value of thermal conductivity play an essential role in boosting the thermoelectric efficiency of the ZrP2 monolayer. The n-type (p-type) monolayerhas a ZT value of 0.78 (1.12) at 500 K. The ZrP2 monolayer is an ideal candidate to be used in the manufacturing of thermoelectric devices.

Transport behavior and thermoelectric properties of SnSe/SnS heterostructure modulated with asymmetric strain engineering

Strain engineering of two-dimensional materials provides specific regulation method for the crystal structure, electric transport behavior and hence thermoelectric properties. Since the layer components of the van der Waals heterojunction exhibit discrepant response to strains, it provides a platform for manipulation of emergent electronic and thermoelectric properties. Here, motivated by the promising thermoelectric materials SnSe and its analogue, we design a specific high-promising thermoelectric candidate based on SnSe-SnS heterostructures, focusing on the strain induced asymmetric bonding-transition and its effect on thermoelectric properties. The compressed SnS/SnSe hetero-bilayer showssignificantly enhanced anisotropic electrical transport properties, due to depressed carrier scattering rate along the robust weak bonding direction. In this armchair direction, extremely high power factor values (3600 μW/cm·K2 for n-type and 4000 μW/cm·K2 for p-type) are predicted at ∼1021 cm−3 at 700 K. We obtain a new state-of-the-art thermoelectric material with extremely high thermoelectric power factor and pave the way for strain engineering of thermoelectric van der Waals heterostructures with robust in-plane weak bonding.

On the Optimal Selection of Flux Barrier Reconfiguration for a Five-Phase Permanent Magnet Assisted Synchronous Reluctance Machine for Low-Torque Ripple Application

This paper aims to investigate the reconfigurations of rotor flux barriers for a five-phase Permanent Magnet Assisted Synchronous Reluctance Machine (PMASynRM). To precisely study the performance of the proposed configurations, a conventional PMASynRM with double-layer flux barriers is included in the study. Since the novel rotor schemes consume the same amount of rare-earth magnets, steel sheet materials, and copper wire, resulting in no extra manufacturing costs, the optimal reconfiguration should be determined, providing developed electromagnetic characteristics. Thus, all the proposed models are designed and analyzed under the same condition. The Lumped Parameter Model (LPM) is exported to the Finite Element Method (FEM) for precise analysis to reach developed torque and lower values of torque ripple. Based on the FEM results the model presenting the lowest torque fluctuations is selected as the optimal model and dynamically investigated. According to the results, in comparison with the conventional model, the introduced rotor designs provide a much lower value of torque fluctuations with a desirable amount of electromagnetic torque and power. In addition, the optimal model presents high values of power factor and efficiency, making it a vital alternative for low-torque ripple high-speed operations with no extra cost to the implementation process.

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.

Structural and electrical studies of Ca0.9Sr0.1MnO3-ZnO nanocomposites

(1-x)Ca0.9Sr0.1MnO3-(x)ZnO (x = 0; 5; 10; 15; 100 wt%) nanocomposites were prepared through solid state mixing method. The ZnO nanoparticles as filler were incorporated into Ca0.9Sr0.1MnO3 matrix. The phase confirmation was carried out using X-ray diffraction. The dc four probe method was performed to characterize the electrical properties. The dispersion of ZnO nanoparticles into the matrix up to 15%wt reduced the electrical resistivity value compared to the pure Ca0.9Sr0.1MnO3 and exhibited semiconductor nature. The differential method (heating mode) was carried out to characterize the thermoelectric properties. The negative values of seebeck coefficient indicate the n-type semiconducting nature of prepared nanocomposites. The 10 wt% of ZnO nano dispersion has the highest power factor value with increment of one order magnitude that of matrix at 673 K. Thus, ZnO nanoparticles dispersion could be an alternative way to improve the thermoelectric performance of Ca0.9Sr0.1MnO3 for medium temperature application.

Enhanced figure of merit of TaIrGe Half-Heusler alloy for thermoelectric applications under the effect of isotropic strain

The structural, electronic and transport properties of the Half-Heusler TaIrGe compound have been reported at different values of tensile and compressive strain using density functional theory (DFT) in conjunction with Boltzmann transport theory. The mechanical and thermodynamical stability of TaIrGe at different values of isotropic strain is confirmed by the calculated value of elastic constants and the phonon dispersion curve, respectively. The electronic structure calculations reveals that the energy bandgap changes significantly on applying tensile and compressive strain. The calculated low value of lattice thermal conductivity (kl) and high value of power factor are key factors in enhancing the performance of resultant thermoelectric material. The calculated value of figure of merit (ZT) for pristine TaIrGe compound is 0.69 and it attains a maximum value (0.82) for 4% tensile strain at T ​= ​1200 ​K, which shows that it can be used as an efficient thermoelectric material under the effect of isotropic strain for high temperature applications.

Interfacial enhancement effect of graphene quantum dots on PEDOT:PSS/single-walled carbon nanotubes thermoelectric materials

In the present study, Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS), with the incorporation of graphene quantum dot (GQD)-coated single-walled carbon nanotubes (SWCNTs), has been used in the preparation of PEDOT:PSS/SWCNTs/GQDs thermoelectric films (PSG). The effect of SWCNTs/GQDs (as a nanofiller) on the microstructure and thermoelectric properties of the composite films has been especially investigated. It was observed that the addition of GQDs will induce a phase separation between PEDOT and PSS. Furthermore, the enhanced interfacial bonding induced a microstructure ordering and an accelerated transport of carriers. The in-plane electrical conductivity and Seebeck coefficient of the obtained film reached 1036 S•cm−1 and 13.8 μV•K−1, respectively, for 1 wt% of SWCNTs/GQDs. These results gave a high power factor (PF) of up to 19.9 µW•m−1•K−2, which is about six times as high as for pristine PEDOT:PSS and also higher than that of PEDOT:PSS/SWCNTs. The obtained maximum ZT reaches 3.22 × 10−3 with high PF value and low in-plane thermal conductivity. The present research provided a new strategy for developing high performance organic thermoelectric materials.

A COMBINATION OF POINT DEFECTS AND NANOSIZED GRAINS TO MINIMIZE LATTICE THERMAL CONDUCTIVITY OF Sn AND Se CO-DOPED CoSb3 VIA MIXED BALL MILLING AND SPARK PLASMA SINTERING

The efficient strategies to minimize thermal conductivity in skutterudite materials are creating point defects along with nanosized grains. In this report, Sn and Se co-doped CoSb3 materials were synthesized through mixed-ball milling and spark plasma sintering techniques to utilize this strategy. Their phases, microstructure and thermoelectric properties were investigated under the content variation of Sn and Se in CoSb3 samples. The experimental results revealed that the Sn and Se were substituted at Sb sites in CoSb3 crystal structure and grain sizes were restricted to a hundred nanometer. The lattice thermal conductivity was reduced to 2.4[Formula: see text]W/mK at 298K. Interestingly, increasing Sn and Se doped content could further minimize the lattice thermal conductivity. The lowest value at room temperature is 1.79[Formula: see text]W/mK for CoSb[Formula: see text]Sn[Formula: see text]Se[Formula: see text] which was dramatically lower than pure CoSb3. Moreover, the increment of Sn and Se content also increased the electrical conductivity of doped samples, while the negative Seebeck coefficient sign tended to decrease. As expected, low electrical conductivity and substantial reduction in the Seebeck coefficient of doped samples at high measurement temperature, resulting in low power factor and low ZT values. It was clearly seen that the highest power factor of 880[Formula: see text][Formula: see text]W/mK2 was found at 516[Formula: see text]K in CoSb[Formula: see text]Sn[Formula: see text]Se[Formula: see text]. Furthermore, it also dominated the highest ZT value of 0.29 at 565 K, compared to the other Sn and Se co-doped samples. From these results, ball milling under dry conditions followed by wet conditions not only allowed a longer milling process but also generated a small fraction of pore which was a part of the reduction in thermal conductivity. Especially, the advantage of the existence of Sn and Se point defects and nanosized grains from this work will be escalated when it was applied to prepare materials that have high power factor values.

Exceptionally high open circuit thermoelectric figure of merit in two-dimensional tin sulphide

Thermoelectric materials with high values of power factor and thermoelectric figure of merit (ZT) are in great demand to make efficient thermoelectric devices. In this work, we explore the thermoelectric transport properties of layered tin sulphide (SnS) using first-principles method combined with Boltzmann transport theory. Our calculations show that the two-dimensional (2D) SnS materials have exceptionally high charge carrier mobilities and low lattice thermal conductivities as compared to other 2D materials such as graphene, phosphorene, MoS2, etc. Consequently, these 2D SnS materials have high power factor and ZT values.

Investigations of the electronic, dynamical, and thermoelectric properties of Cd1-xZnxO alloys: First-principles calculations

The structural, dynamical, electronic and thermoelectric properties of rock-salt and wurtzite Cd1-xZnxO alloys were investigated using the density functional theory (DFT). In addition, the semi-classical Boltzmann transport theory was utilized to evaluate the thermoelectric properties with the constant relaxation time approximation. The alloys were found to exhibit a semiconducting behavior with direct and indirect band gaps in their wurtzite and rock-salt structures, respectively, based on the hybrid GGA-mbj functional. The highest Seebeck coefficient values were obtained at 300 K, whereas the highest power factor values were found at 1200 K for all structures. This behavior is promising for thermoelectric applications at high temperatures.

Touch sensor and photovoltaic characteristics of CuSbS2 thin films

Spin-coated chalcostibite CuSbS2 thin films (≈500 nm thick) were fabricated and the influence of the drying temperature on the structural, morphological, optical and thermoelectric properties of the films was investigated. Crystalline phase-pure chalcostibite has been obtained for the films dried at 180 °C and 210 °C, while below 180 °C these films are partially amorphous. Surprisingly, at drying temperature of 240 °C, a CuxS secondary phase appeared. The increase of the drying temperature leads to the increase of the particle size and the decrease of the optical band gap, which is interesting for optoelectronic applications. The highest power factor value was achieved for the film dried at 210 °C, due to the inexistence of secondary phases, which allowed realizing a stable thermoelectric touch sensor with a Vsignal/noise of 5. In addition, this film was tested as a photovoltaic (PV) device and a power conversion efficiency (PCE) of 0.030% with an open-circuit voltage (VOC) of 0.36 V, a short-circuit current density (JSC) of 0.278 mAcm−2 and a fill factor (FF) of 0.27 were obtained. Therefore, this work evidences a pathway toward developing bi-functional devices with simultaneously thermoelectric touch sensor and photovoltaic functions.

Exploring the High-Temperature Electrical Performance of Ca3−xLaxCo4O9 Thermoelectric Ceramics for Moderate and Low Substitution Levels

Aliovalent substitutions in Ca3Co4O9 often result in complex effects on the electrical properties and the solubility, and impact of the substituting cation also depends largely on the preparation and processing method. It is also well-known that the monoclinic symmetry of this material’s composite crystal structure allows for a significant hole transfer from the rock salt-type Ca2CoO3 buffer layers to the hexagonal CoO2 ones, increasing the concentration of holes and breaking the electron–hole symmetry from the latter layers. This work explored the relevant effects of relatively low La-for-Ca substitutions, for samples prepared and processed through a conventional ceramic route, chosen for its simplicity. The obtained results show that the actual substitution level does not exceed 0.03 (x < 0.03) in Ca3−xLaxCo4O9 samples with x = 0.01, 0.03, 0.05 and 0.07 and that further introduction of lanthanum results in simultaneous Ca3Co4O9 phase decomposition and secondary Ca3Co2O6 and (La,Ca)CoO3 phase formation. The microstructural effects promoted by this phase evolution have a moderate influence on the electronic transport. The electrical measurements and determined average oxidation state of cobalt at room temperature suggest that the present La substitutions might only have a minor effect on the concentration of charge carriers and/or their mobility. The electrical resistivity values of the Ca3−xLaxCo4O9 samples with x = 0.01, 0.03 and 0.05 were found to be ~1.3 times (or 24%) lower (considering mean values) than those measured for the pristine Ca3Co4O9 samples, while the changes in Seebeck coefficient values were only moderate. The highest power factor value calculated for Ca2.99La0.01Co4O9 (~0.28 mW/K2m at 800 °C) is among the best found in the literature for similar materials. The obtained results suggest that low rare-earth substitutions in the rock salt-type layers can be a promising pathway in designing and improving these p-type thermoelectric oxides, provided by the strong interplay between the mobility of charge carriers and their concentration, capable of breaking the electron–hole symmetry from the conductive layers.

High thermoelectric performance of high‐mobility Ga‐doped ZnO films via homogenous interface design

AbstractGa‐doped ZnO (GZO) thin films grown on sapphire substrates have been widely investigated as a promising transparent thermoelectric (TE) material. However, due to the large lattice mismatch and thermal expansion between the sapphire substrate and GZO film, strain‐induced lattice distortion impedes the transport of electrons, leading to low carrier mobility. In this study, ZnO homo‐buffer layers with different thicknesses were inserted between sapphire substrates and GZO films, and their effect on the TE properties was investigated. A thin ZnO interlayer (10 nm) effectively reduced the lattice mismatch of the GZO film and improved the carrier mobility, which contributed to the large enhancement in the electrical conductivity. Simultaneously, energy filtering occurred at the interface between GZO and ZnO, resulting in a relatively high density of states (DOS) effective mass and maintaining a high Seebeck coefficient compared to that of the unbuffered GZO films. Consequently, the GZO film with a 10 nm thick ZnO buffer layer possessed a high power factor value of 449 μW m−1 K−2 at 623 K. This study provides a facile and effective method for optimizing the TE performance of oxide thin films by synergistically improving their carrier mobility and enhancing their effective mass.

Structural stability and thermoelectric properties of new discovered half-Heusler KLaX (X = C, Si, Ge, and Sn) compounds

Structural, elastic, electronic, and thermoelectric properties of KLaX (X = C, Si, Ge and Sn) half Heusler compounds have been studied using the full potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). It is shown that the KLaX half Heusler compounds are energetically and mechanically stable. The calculated band structure estimates with modified Becke-Johnson (mBJ) potential, indicates a semiconducting nature with direct band gaps of 0.76 eV, 0.79 eV, and 0.81 eV for KLaC, KLaSn, and KLaX (X = Si and Ge) respectively. The valence band of KLaX is more influenced by spin-orbit coupling than in the conduction band. The Seebeck coefficient (S), electronic conductivity (σ), electronic thermal conductivity (κe), figure of merit (ZT) and the power factor (PF) have been investigated using the semi-classical Boltzmann transport theory with rigid band theory. The KLaX half Heusler compounds exhibit high thermopower values and p-type charge carriers for their thermoelectric performance than electron doping. Including the spin-orbit coupling in our calculations increases the flatness of the valence band from X = Si to Sn. The high values of ZT and PF of KLaX half-Heusler compounds make it promising materials for thermoelectric applications.

Optimized Mn and Bi co-doping in SnTe based thermoelectric material: A case of band engineering and density of states tuning

Tin telluride (SnTe) overwhelmingly continues to be studied owing to its promising thermoelectric properties, tunable electronic structure, and its potential as an alternate to toxic lead telluride (PbTe) based materials. In this research, we engineer the electronic properties of SnTe by co-doping Mn and Bi below their individual solubility limit. The First principles density functional theory studies reveal that both Bi and Mn introduce resonance states, thereby increasing the density of states near the Fermi level leading to enhanced Seebeck coefficient. This unique combination of using two resonant dopants to introduce flatter bands is effective in achieving higher performance at lower temperatures manifesting into a large Seebeck value of ∼91 μV/K at room temperature in the present case. Both elements optimally co-doped results in a very high power factor value of ∼24.3 μW/cmK2 at 773 K when compared to other high performance SnTe based materials. A zT of ∼0.93 at 773 K is achieved by tuning the proportion of the co-dopants Mn and Bi in SnTe. The hardness value of pristine SnTe was also seen to increase after doping. As a result, synergistic optimized doping proves to be a suitable means for obtaining thermoelectric materials of superior characteristics without the need for heavy doping.

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.

The structures and thermoelectric properties of Zn-Sb alloy films fabricated by electron beam evaporation through an ion beam assisted deposition

Zn-Sb alloys are potential low-cost and non-toxic p-type thermoelectric materials for applications in the temperature range between 300 and 700 K. In this experiment, Zn-Sb alloy films were prepared by electron beam evaporation through an ion beam assisted deposition (IBAD). Our studies have confirmed that the structural phase, chemical composition, chemical binding, carrier concentration and microstructures of the film can indeed be effectively controlled by the voltage and current of the ion beam. Particularly, the carrier concentration of the film will rise along with the increase of the argon ion beam current. When the ion beam currents are set at 0.2–0.6 A, the carrier concentrations of the films can be controlled at around 1019–1020 cm−3, which fall within the optimal carrier concentration range for Zn-Sb based thermoelectric materials. The temperature dependence of Seebeck coefficient and the electrical conductivity of the films were measured to evaluate their thermoelectric performance. The results indicate that the film with Zn4Sb3 + ZnSb mixed phase will have better thermoelectric properties. A high power factor value of ~1280 μW/m-K2 is obtained in the films assisted by the ion beam current of 0.6 A. Our results demonstrate that the IBAD technique is extraordinary promising to fabricate Zn-Sb films with excellent thermoelectric performance and can be used to produce other potential thermoelectric materials.

Study of thermoelectric properties of Sr0.92A0.08TiO3 (A=Yb / Tm) perovskite oxide using density functional theory method

The first principle methods have been employed to investigate electronic and thermoelectric properties of Sr0.92Yb0.08TiO3 and Sr0.92Tm0.08TiO3 perovskite-oxide based molded samples. Generalized gradient approximation (GGA) with Hubbard U parameter is used by WIEN2k code for the calculations. The straight band line was observed in the band structure of both studied samples. This was generated from 4f-orbitals as shown in partial density of state diagrams. It is also noticed that Yb and Tm doped in SrTiO3 changed the perovskite-based oxide from a wideband insulator to metallic nature. A thermoelectric power factor of Sr0.92Tm0.08TiO3 sample is higher than that of Sr0.92Yb0.08TiO3, this is as a result of its huge electrical conductivity. The dependent of chemical potential to temperature was revealed in the study where high value of power factor was recorded for high temperature.

Realizing high thermoelectric performance in p-type Si1-x-yGexSny thin films at ambient temperature by Sn modulation doping

In this study, we report a power factor (PF) value as high as 1950 μW m−1 K−2 for B-ion implanted thermoelectric Si1-x-yGexSny ternary alloy films at ambient temperature by radio frequency sputtering followed by a short-term rapid thermal annealing heat treatment. The record high PF value was realized by modulation doping of Sn in the Si1-x-yGexSny film. It was found that using metallic Sn as nanoparticles and Si1-x-yGexSny as the matrix leads to a large enhancement of the carrier concentration and a very small decrease in carrier mobility. As a result, the electrical conductivity and power factor of the modulation doped Si1-x-yGexSny alloy were greatly improved. The findings of this study present emerging opportunities for the modulation of Si integration thermoelectrics as wearable devices charged by body temperature.