Variation Of Seebeck Coefficient Research Articles

Mechanism of Seebeck coefficient variation at the output of NiCr/NiSi thin film thermocouple with different wires

In this paper, by using magnetron sputtering to prepare NiCr/NiSi thin film thermocouples, the static calibration method is used for NiCr/NiSi thermocouples with rapid temperature calibration experiments. Different temperature calibration curves are obtained. The Seebeck coefficient of NiCr/NiSi thin film thermocouples connected to NiCr/NiSi wires is significantly higher (41.39 μV/°C) than that of NiCr/NiSi wires (0 μV/°C). The Seebeck coefficient (41.39 μV/°C) of the NiCr/NiSi thin-film thermocouple connected to copper wire is significantly higher than that of the thermocouple connected to copper wire (0 μV/°C). The problem of the Seebeck coefficient of the K-type thermocouple is analyzed by experimental data, which provides the relevant parameter basis for the use of the K-type thermocouple. The method has the advantages of simple equipment, convenient operation, accurate and reliable data, and provides a basis for the sensor to measure the temperature measurement.

Function Graded Carbon Micro‐Structures for Powerless Photon Sensing with Intriguing µm‐Scale Position Sensitivity

AbstractPartial laser treatment is introduced to carbon‐based microfibers to generate excellent photon sensing capability without bias. This treatment brings about a Seebeck coefficient distribution along the sample's length, out of which a photovoltage with no external bias is generated and sensed. Using a line‐shaped laser spot, carbon microfiber (CMF), graphene microfiber (GMF), and graphene aerogel fiber (GAF) are investigated for their response to µm‐scale photon irradiation. A higher sensitivity for the incident photon is found for the GAF with no position sensitivity. More Seebeck coefficient variation is also observed for the GAF considering the amount of laser power used for the laser treatment. A weaker Seebeck coefficient spatial variation is observed for the GMF compared with the GAF. However, its photovoltage shows an abrupt magnitude change from the laser‐treated region to the non‐treated one. Despite the low spatial variation of the Seebeck coefficient for the CMF, it features an excellent and accurate position‐sensitive photoresponse with polarization change over a distance of ≈100 µm. Such unique capability prompts novel applications in using partially annealed CMF for sensing the position of optical beams at the microscale.

Comparative study between pure and manganese doped copper sulphide (CuS) nanoparticles

The pure CuS and Mn2+ doped CuS nanoparticles are synthesized by wet chemical route. The CuS phase and hexagonal crystal structure is confirmed by the powder X-ray diffraction and Raman analysis. The vibrational bonds present in the respective synthesized samples are confirmed by Fourier transformed infra-red spectroscopy. The spherical shapes of the nanoparticles are validated by the electron diffraction in scanning and transmission mode. The thermal analysis showed the Mn2+ doped CuS nanoparticles to be more stable than pure CuS nanoparticles. The thermal parameters determined using Coats-Redfern relation stated thermal activation energy and enthalpy change values are highest in the higher temperature range. The Seebeck coefficient variation with temperature and ambient condition Hall effect measurements showed the synthesized nanoparticles to be semiconducting and p-type in nature. The magnetic properties study by Gouy method showed the nanoparticles to be paramagnetic.

Improved room-temperature thermoelectric characteristics in F4TCNQ-doped CNT yarn/P3HT composite by controlled doping

Abstract High room-temperature thermoelectric performance is important for low-grade waste heat power generation as there are plenty of heat thrown away uselessly in our daily life, most of which are below 100 °C. However, most of the thermoelectric materials are limited to high temperature application. In this work, room-temperature thermoelectric power factor of carbon nanotube (CNT) yarn is improved by controlled doping, which is achieved by making composite with poly 3-hexylthiophene −2, 5-diyl (P3HT) followed by doping with 2, 3, 5, 6-tetrafluo-7, 7, 8, 8-tetracyanoquinodimethane (F4TCNQ). The temperature-dependent Seebeck coefficient based on power–law model suggests that P3HT shifts the Fermi energy of CNT yarn towards the valence band edge, and reduces the ionic scattering and carrier relaxation time. As a result, the Seebeck coefficient is increased while the variation of Seebeck coefficient with temperature is reduced, and hence, the room-temperature thermoelectric power factor is improved. With controlled doping, the power factor of CNT yarn/P3HT composite reaches to 1640–2160 μW m−1K−2 at the temperature range of 25–100 °C, which is higher than that of CNT yarn alone.

High-energy laser detection through thermoelectric generators

Detection of high-energy laser strikes is key to the survivability of military assets in future warfare. The introduction of laser weapon systems demands the capability to quickly detect these strikes without disrupting the stealth capability of military craft with active sensing technologies. We explored the use of thermoelectric generators (TEGs) as self-powered passive sensors to detect such strikes. Experiments were conducted using lasers of various power ratings, wavelengths, and beam sizes to strike 2 × 2 cm2 commercially available TEGs arranged in different configurations. Open-circuit voltage and short-circuit current responses of TEGs struck with 808-, 1070-, and 1980-nm lasers at irradiance levels between 8.5 and 509.3 W / cm2 and spot sizes between 2 and 8 mm are compared. TEG surface temperatures indicate that the sensor can survive temperatures nearing 400°C. TEG open-circuit voltage magnitudes correlate more strongly with net incident laser power than with specific irradiance levels, and linearity is limited by Seebeck coefficient variation with temperature. Open-circuit voltage responses are characterized by 10% to 90% rise times of ∼2 to 10 s despite surface temperatures not reaching equilibrium. With open-circuit voltage as the sensing parameter, detection thresholds three times above the standard deviation noise level can be exceeded within 300 ms of the start of a laser strike with irradiance levels of ∼200 W / cm2. Potential harvested power levels as high as 16 mW are estimated based on measured electrical responses. A multiphysics finite-element model corresponding to the experiments was developed to further optimization of a lightweight, low-profile TEG sensor for detection of high-energy laser strikes.

Density functional theory study of electronic, optical and transport properties of magnesium based MgY2Z4 (Z = S and Se) spinels

Magnesium based spinel chalcogenides MgY2Z4 (Z = S and Se) have recently become a focus of renewed research interest owing to their high magnesium mobility; making them potential candidates for Mg batteries. In addition, the existence of a >1 eV band gaps in MgY2Z4 compounds also make them interesting for opto-electronic device operating in the visible to UV range of electromagnetic spectrum. Our calculations indicate that the electronic properties computed using the mBJ-LDA + SOC are in good agreement with earlier DFT calculations. The optical properties of the two compounds are examined as a function of incident photon energy, which indicate that these materials can be utilized in optical devices operating in visible and UV region of electromagnetic spectrum. The transport properties are also computed using BoltzTrap code where the variation of electrical conductivity, thermal conductivity and Seebeck coefficient with chemical potential and temperature is examined.

Solvent‐Mediated n‐Type Doping of SWCNTs to Achieve Superior Thermoelectric Power Factor

AbstractCarbon nanotubes (CNTs) have been demonstrated as promising candidates for thermoelectrics (TEs) owing to their excellent electrical and mechanical properties. Here a new dopant to obtain flexible n‐type CNT‐based TE films from solution is reported. By doping single‐walled carbon nanotubes (SWCNTs) with tetrabutylammonium bromide (TBAB), p‐type nanotubes can be successfully converted to n‐type form, which is confirmed by both Raman and X‐ray photoemission spectroscopy (XPS) spectra. Furthermore, the influences of doping concentration and dispersion medium on TE properties are investigated. The optimal n‐type SWCNT films fabricated in N,N‐dimethylformamide (DMF) solvent exhibit an impressive power factor of 339 µW m−1 K−2 and excellent air stability by less than 10% variation of Seebeck coefficient during 192 h at room temperature without encapsulation, both of which are among the hitherto highest reported. This work sheds light on the interaction between TBAB molecules and SWCNTs in different dispersion media and offers a guideline for efficient n‐doping of SWCNT based TE materials.

Thermoelectric Power, Electrical Resistivity and Magnetic Properties of Ni-Sm Nano-particles

Nanocrystalline Samarium doped Nickel ferrites having compositional formula NiSmXFe2-XO4 (0.00≤X≥0.10) were prepared by the citrate-gel auto combustion method and sintered at 5000C. The structural characteristics such as XRD analysis were shown cubic spinel structure, and the structural parameters like lattice parameter, X-ray density, bulk density, and porosity variations with Sm doping were studied. The surface morphology of prepared samples was observed by Scanning Electron Microscopy (SEM). The magnetic parameters were studied at room temperature with VSM, and the observed results are discussed with composition. The DC electrical properties were studied using a two-probe method in the temperature range from room temperature to well beyond Curie temperature. Thermoelectric power studies were carried out from room temperature to well beyond transition temperature with a differential method. The Seebeck coefficient variation with temperature was studied, and it shows the prepared samples are classified as n-type semiconductors. The observed results can be explained on the basis of the conduction mechanism.

Strain and electric field dependent variation in electronic and thermoelectric properties of PtS2

Ab initio calculations based on plane wave methods show that the band gap of PtS2 depends on the number of monolayers combined by van der Waals (vdW) interactions or spin orbit correction (SOC). The valence band minimum (VBM) is sensitive to the out-of-plane, and conduction band maximum (CBM) to the in-plane lattice constants. The vdW force enhances the bonding out of plane, which in turn influences the bonding in plane. The band diagram gets splitted on application of SOC and hence resulting in decrease of band gap. On application of biaxial compressive and tensile strain, a variation in band gap from 1.54 eV to 1.08 eV & 0.97 eV and 1.06 eV & 1.04 eV is observed in case of bilayers with different stackings (AA & AB) respectively. A variation in band gap from 1.54 eV to 0.16 eV (0.23 eV) is also observed on applying electric field on AA(AB) bilayers of PtS2 in z-direction. Absence of imaginary frequencies in phonon dispersion of strained structure reflects the dynamical stability of the studied structure. The effects of strain on the thermoelectric properties of PtS2 monolayer and bilayer were also studied. A variation in the electrical conductivity is observed with the increase in strain in bilayers. As expected for thermoelectric application, the trend in the variation of Seebeck coefficient is of opposite nature. The present work demonstrates the flexibility available for tuning the electronic and thermoelectric properties of this material for a wide range of applications.

Experimental and Simulation Studies on Thermoelectric Cooler: A Performance Study Approach

The current experimental and simulation studies focus on two distinctive approaches on developing performance specifications on a typical thermoelectric cooler. The performance specifications considered for the current study involves cooling capacity, voltage, and current for different temperature ranges on hot side of the module. Simulation studies were carried out using COMSOL Multiphysics software for analyzing the coefficient of performance (COP). Thermoelectric cooler’s performance was simulated for the module’s hot side temperature ranges of about 303.15–333.15 K with a stipulated temperature interval of around 5 K. COP is evaluated at various temperature ranges (20 K, 40 K, and 60 K) over the module for each temperature prevailing on the hot side. The whole system is numerically modeled and the final attained results were correlated with the results obtained from simulation. Factors considered for modeling includes Seebeck coefficient, thermal conductivity, and resistivity variation of the Peltier elements.

Exploration of highly correlated Co‐based quaternary Heusler alloys for spintronics and thermoelectric applications

The half-metallic character of new quaternary Heusler alloys CoXMnAs (X = Ru, Rh) is established along with their thermoelectric, mechanical, and thermodynamic properties. The optimization of energy suggests that alloys are stable in Y2-type structure with a ferromagnetic character. The electronic band profile through generalized gradient approximation and modified Becke-Johnson potential indicates the metallic character of alloys. However, with inclusion of Hubbard potential to generalized gradient approximation, the alloys depict half-metallic character with semiconducting nature in spin-down state. The alloys possess high magnetic moment, CoRuMnAs has 5 μB, whereas CoRhMnAs has 6 μB, following Slater-Pauling rule MT = ZT − 24. The narrow band gap in spin-down channel enhances the thermoelectric properties. The maximum value for thermopower (|S|) obtained is 44.3 and 53.44 μV/K for CoRuMnAs and CoRhMnAs, respectively. The variation of electrical conductivity, Seebeck coefficient, and figure of merit affirm increasing trend with temperature, which is a good indication of materials to be used in thermoelectric technology. The mechanical stability along with ductile nature of alloys is determined through elastic constants. Further, we have calculated thermodynamic properties and have established their dependence on temperature and pressure using quasi-harmonic Debye model. The half-metallic nature with efficient thermoelectric parameters strongly supports the possible application of alloys for spin devices and green energy generation.

Performance study of thermoelectric cooler using multiphysics simulation and numerical modelling

ABSTRACT This paper focuses on two different methods of obtaining performance parameters of a thermoelectric cooler. Based on the simulation results using COMSOL Multiphysics the performance parameters, such as maximum cooling capacity, maximum current and voltage for various temperatures on the hot side of module and coefficient of performance (COP) for various temperature differences across the module, are obtained. The system has been simulated for temperature of the hot side ranging from 303.15 K to 333.15 K with an interval of 5 K. Coefficient of performance is obtained for a temperature difference of 20 K, 40 K and 60 K across the module for every value of temperature condition on the hot side of module. The system is also modelled numerically and the results obtained are compared with the simulated results. The variation of resistivity, seebeck coefficient and thermal conductivity of Peltier elements with temperature variations are considered for numerical modelling.

Thermoelectric response of ZrNiSn and ZrNiPb Half-Heuslers: Applicability of semi-classical Boltzmann transport theory

Abstract We investigated the thermoelectric transport mechanism of ZrNiSn and ZrNiPb Half-Heuslers within the Boltzmann transport theory, under constant relaxation time approximation. The prediction of band structure behavior along the high symmetry Brillouin zone and density of states are used to establish relations among various transport coefficients like Seebeck coefficient, electrical conductivity, thermal conductivity and power factor which have been found to be in good agreement with the experimental results. The Seebeck coefficient variation show the n-type behavior of heat carriers. The electrical and thermal conductivity show a semiconducting nature of bands along the Fermi level. The lattice part of thermal conductivity show an exponential decreasing trend along the high temperatures. Power factor variation and figure of merit show the heavier element doping of ZrNiSn results in descent increase in efficiency triggering its applicability. The overall measurements show that semi classical Boltzmann transport theory has well behaved potential in predicting the transport properties of the compounds.

Insight into structural, electronic and thermoelectric properties of Zr2MnX (X = Ga, In) Heuslers

Spin polarized analysis of band structure, magnetism and thermoelectric properties of Zr2MnX (X = Ga, In) alloys have been carried out within DFT and post-DFT techniques. The structural properties show the F-43m phase as the stable phase with optimized lattice parameters as 6.58 and 6.69 Å, respectively. The band structure calculation shows spin gapless semiconducting behavior with negligible magnetic moments according to Slater-Pauling rule. The transport properties were investigated to find the stand of alloys for thermoelectric use. Seebeck coefficient variation define them as n-type materials, with descent value of electrical conductivity. The absolute values of Seebeck coefficient found at room temperatures are 35.54 μV K−1 and 32.93 μV K−1. The power factor variation was used to check the efficiency, which varies from 0.92(0.04) × 10−4 W K−2 m at 50 K to 12.53(7.0) × 10−4 W K−2 m at 500 K, respectively for Zr2MnX (X = Ga, In). The overall peculiar electronic behavior together with thermoelectric efficiency finds their applications in spintronics and room temperature waste heat recovery systems.

Carrier Transport and Thermoelectric Properties of Differently Shaped Germanene (Ge) and Silicene (Si) Nanoribbon Interconnects

Here, we report a study of carrier transport and thermoelectric properties of silicene/germanene nanoribbon (SiNR/GeNR) interconnects of varying shapes (namely, “V,” “L,” “U,” and “S” shaped) with empirical tight binding—nonequilibrium Green’s function approach. Our simulation shows that a significant reduction in both electron and phonon transmission in such differently shaped NRs compared to perfect ones. In terms of thermoelectric properties, Seebeck coefficient ( $\mathbb {S}$ ) variation in the range of −72.3 to $3.52~\mu \text{V}$ /K at 300 K for SiNR and −176 to $-\textsf {95.5}\,\,\mu \text{V}$ /K at 300 K for GeNR is observed in different pattern conditions. For Peltier coefficient ( $\pi $ ), these ranges are −0.23 to 0.001 V for SiNR and −0.053 to −0.011 V for GeNR at 300 K. Simulation also shows significant change in thermoelectric figure of merit ( $\textit {ZT}$ ) for a different pattern and temperature with peak $\textit {ZT}~0.09$ at 800 K for “U”-shaped SiNR and 0.80 at 400 K for “L”-shaped GeNR.

Effect of bismuth doping on thermoelectric properties of Sr2TiCoO6

ABSTRACTOxides are considered as one of the most promising materials for thermoelectric applications because of their environmental-friendly nature, lower processing cost and better stability at high temperature compared to other intermetallic compounds and alloys. Recently SrTiO3 based perovskites and double perovskites have shown promising thermoelectric properties especially at high temperature. In this report, the prospect of Sr2TiCoO6 based double perovskites modified by aliovalent substitution of Bi+3 in Sr-site has been evaluated for high temperature thermoelectric applications. BixSr2-xTiCoO6 (0 ≤ x ≤ 0.2) ceramics have been synthesized by solid state reaction method. Dense ceramic samples have been characterized to inspect their crystal structure and microstructure using X-Ray Diffraction and Scanning Electron Microscopy, respectively. The Seebeck coefficient (S) and electrical conductivity (s) variations with temperature for all the compositions have been measured in the temperature range from 323 K to 1073 K. The electrical conductivity has been increased to nearly double in magnitude with bismuth substitution in Sr2TiCoO6 as a result of more electronic defects created by aliovalent doping in these oxides. The maximum conductivity (∼ 3917 S/m) has been obtained for the composition Bi0.2Sr1.8TiCoO6 at 760 K resulting enhanced thermoelectric power factor in this composition. With increase in bismuth content, the semiconductor to metal transition (TMS) was found to be shifted towards higher temperature in these double perovskites. Furthermore, the charge transport mechanism in these compositions has been elucidated with respect to variable range hopping and small polaron hopping conduction models.

Seebeck Coefficient Measurement and Its Narrow Band Model Interpretation in FeTe0.5Se0.5 Superconductor

We have measured Seebeck coefficient (S) of FeTe0.5Se0.5 superconducting sample from 10 to 300 K. The variation of Seebeck coefficient with temperature of this system was found to be very anomalous, and the overall experimental observation of the S(T) was studied in the outline of a narrow-band model. In high-temperature region, the Seebeck coefficient is almost independent of temperature. Further, from the study of high-temperature magnitude of S, sample undergoes a change in sign in the Seebeck coefficient, wherein, appearance of a negative peak around 22 K and subsequently, its Seebeck coefficient goes to zero in the superconducting transition temperature regime around 11 to 13 K. It is revealed that the bandwidth and a small asymmetry involved in narrow bands give a realistic explanation to the anomalous temperature dependence of Seebeck coefficient of FeTe0.5Se0.5 system.

Thermoelectric properties of (1-x)LaCoO3.xLa0.7Sr0.3MnO3 composite

We report the thermoelectric (TE) properties of (1-x)LaCoO3.xLa0.7Sr0.3MnO3 (0 < x < 0.50) composite in a temperature range 320–800 K. Addition of La0.7Sr0.3MnO3 to LaCoO3 in small amount (5 weight %) improves the overall Seebeck coefficient (α) at higher temperatures. The electrical conductivity however decreases due to a decrease in carrier concentration of the composite. The decrease in electrical conductivity of the composite at high temperature may be attributed to the insulating nature of the LSMO above room temperature. Thermal conductivity (κ) of all the samples increases with an increase in the temperature, but decreases with increasing LSMO content. We also report the local variation of Seebeck coefficient across the composite samples measured using a precision Seebeck measurement system. A maximum value of 0.09 for the figure of merit (ZT) is obtained for 0.95LaCoO3.0.05La0.7Sr0.3MnO3 at 620 K which is significantly higher than the ZT of either of LaCoO3 or La0.7Sr0.3MnO3 at 620 K. This suggests the potential for enhancement of operating temperatures of hitherto well known low temperature thermoelectric materials through suitable compositing approach.

On the nature of the (de)coupling of the magnetostructural transition in Er5 Si4

In this report, a successful thermodynamical model was employed to understand the structural transition in Er$_5$Si$_4$, able to explain the decoupling of the magnetic and structural transition. This was achieved by the DFT calculations which were used to determine the energy differences at 0 K, using a LSDA+U approximation. It was found that the M structure as the stable phase at low temperatures as verified experimentally with a $\Delta F_0 = -$0.262 eV. Finally, it was achieved a variation of Seebeck coefficient ($\sim$ 6 $\mu$V) at the structural transition which allow to conclude that the electronic entropy variation is negligible in the transition.

Spin-orbit coupling induced structural stability and semi-metallic state in La3 Ir3 O11

La3 Ir3 O11 crystallizes in a cubic symmetry with its structure composed of electronically active IrO6 octahedral motifs, which are corner and edge shared. Empirical considerations suggest Ir to be in the +4.33 valence state in La3 Ir3 O11, thereby anticipating the material to be a good conductor primarily due to the presence of holes in the crystal field split t2g bands of the Ir 5d manifold. However, a comprehensive investigation of the electronic structure by means of first principles calculations find La3 Ir3 O11 to be a spin-orbit driven semi-metallic iridate, with its Fermi energy comprised of both hole and electron bands. The properties of the electron-hole asymmetry in La3 Ir3 O11 is clearly manifested in the temperature dependent variation of electrical conductivity and Seebeck coefficient, which are calculated using the Boltzmann transport theory. Besides, finding that Fermi energy is positioned in a steep valley like feature in the density of states spectra, the calculations also predict that both hole and electron doping would induce a semi-metal to metal transition in La3 Ir3 O11.