Thermoelectric Potential Research Articles

Thermoelectric properties of LiCo1−xMxO2 (M = Cu, Mg, Ni, Zn): Comparison with LiyCoO2 and NayCoO2 systems

LiyCoO2 has a similar layered structure to NayCoO2, which is a typical p-type oxide thermoelectric material, and the average Co valence of 3 + y is controlled by the Li content y. We investigated the thermoelectric properties of LiCo1−xMxO2 samples (M = Cu, Mg, Ni, Zn) for the first time at high temperatures, in which Co3+ was substituted by the divalent M2+ ions, and the average Co valence of 3 + x can be controlled similarly to the Li content y in LiyCoO2. The substitution of the M2+ ions for the Co site was found to show thermoelectric properties similar to those of LiyCoO2 with the same average Co valence. The Mg-doped sample showed the highest thermoelectric performance at high temperatures in this study; the thermoelectric power factor P is 2.38 × 10−4 W m−1 K−2 at 1173 K and the dimensionless figure of merit ZT is 0.024 at 876 K. The thermoelectric potential of LiCo1−xMxO2 is discussed and compared with those of LiyCoO2 and NayCO2 systems.

Micro-Thermoelectric Generation Modules Fabricated with Low-Cost Mechanical Machining Processes

Micro/small-scale thermoelectric generation modules are able to produce continuous, noise-free and reliable electricity power using low temperature differences that widely exist in nature or industry. These advantages bring them great application prospects in the fields of remote monitoring, microelectronics/micro-electromechanical systems (MEMS), medical apparatus and smart management system, which often require a power source free of maintenance and vibration. In this work, a prototypical thermoelectric module (12 mm × 12 mm × 0.8 mm) with 15 pairs of micro-scale thermoelectric legs (0.2 mm in width and 0.6 mm in height for each leg) is fabricated using a low-cost mechanical machining process. In this process, cutting and polishing are the main methods for the preparation of thermoelectric pairs from commercial polycrystalline materials and for the fabrication of electrode patterns. The as-fabricated module is tested for its power generation properties with the hot side heated by an electrical heater and the cold side by cold air. With the heater temperature of 375 K, the thermoelectric potential is about 9.1 mV, the short circuit current is about 14.5 mA, and the maximum output power is about 32.8 μW. The finite element method is applied to analyze the heat transfer of the module during our test. The temperature difference and heat flux are simulated, according to which the output powers at different temperatures are calculated, and the result is relatively consistent compared to the test results.

Enhanced Electronic Transport Properties of Se-Doped SnTe1−xSex Nanoparticles by Microwave-Assisted Solvothermal Method

Pure lead-free SnTe has limited thermoelectric potentials because of its low Seebeck coefficients and its relatively large thermal conductivity. Herein, we report on the enhanced electronic transport properties of selenium (Se) doped tin telluride (SnTe1−xSex) nanoparticles (NPs) synthesized by a rapid microwave-assisted solvothermal method and subsequent spark plasma sintering (SPS). Se-doped SnTe NPs, consisting of regular octahedral NPs with sizes from 1.5 μm to 300 nm, are synthesized with sufficient Se doping contents, and detailed structural characterizations reveal a large fraction of grain boundaries in our nanostructures, which is conducive to phonon scattering. Here we demonstrate that it is possible to enlarge the band gap by tuning the doping and composition, ultimately enhancing the power factor. As a result, a power factor value of ∼10.45 μW/cmK2 is attained at 773 K for the SnTe0.97Se0.03 sample, which is 35% higher than that of an undoped SnTe sample. This synthesis and assembly approach provides strategic guidance for maximizing the power factor by nanocrystallization and doping.

Thermoelectric Properties of Polycrystalline n-Type Pb5Bi6Se14

Chalcogenides are currently receiving attention due to their interesting thermoelectric properties that stem from their complex crystal structures and semiconducting properties. Here, we report on the synthesis and measurements of the transport properties in a broad temperature range (2–723 K) of polycrystalline n-type Pb5Bi6Se14, a member of the homologous series (PbSe)5(Bi2Se3)3m (m = 1), to assess its thermoelectric potential and to shed light on the basic mechanisms governing the low-temperature transport. The anisotropic crystal structure gives rise to transport properties that differ on samples measured parallel or perpendicular to the pressing direction. The measurements show that this compound exhibits semiconducting-like properties with thermopower values that reach 250 μV K−1 at 723 K. The lattice thermal conductivity values are very low in the whole temperature range (∼0.5 W m−1 K−1) and close to the theoretical minimum thermal conductivity estimated from sound velocities. Thanks to this remarkable property, a peak ZT of 0.5 is achieved at 720 K.

Metallo‐organic n‐type thermoelectrics: Emphasizing advances in nickel‐ethenetetrathiolates

ABSTRACTMetallo‐organic complexes with nickel as the metal center have been shown to exhibit high electrical conductivities warranting investigation of their thermoelectric potential. A review of metallo‐organic n‐type thermoelectrics is presented with a focus on nickel‐sulfur coordination compounds. Herein, we also investigate the extent of oxidation on thermoelectric properties of poly(Ni‐1,1,2,2‐ethenetetrathiolate) (Ni‐ETT) based materials. Elemental analysis and X‐ray photoelectron spectroscopy are used to characterize samples with different air exposure times, leading to differing levels of oxidation. When blended with an inert polymer matrix, the sample exposed to air for 30 min resulted in an eight times enhancement in electrical conductivity compared to the sample exposed to air for 24 h. Furthermore, the elemental composition of the 30 min sample fit the empirical formula Ax(MC2S4) postulated in literature, while the 24 h sample does not, which we attribute to decomposition during the oxidation process and presence of disulfides. The Seebeck coefficient remains largely unchanged as a function of oxidation time, indicating that this may be a viable technique to decouple Seebeck and electrical conductivity for high‐performance organic thermoelectric materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44402.

High thermoelectric potential of n-type Pb1−xTixTe alloys

In an attempt to reduce the reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of n-type Pb1−xTixTe alloys, with x values of up to 3%. A solubility limit of 0.5 at. % Ti in PbTe was identified, while beyond this composition, a precipitation of a TiTe2 phase was occurred. An impressive maximal dimensionless thermoelectric figure of merit ZT of ∼1.2 was obtained upon 0.1% Ti doping at 500 °C, indicating a ∼9% efficiency enhancement compared to an undoped PbTe. It is shown that generating a functionally graded material based on undoped PbTe as a low temperature segment and a 0.1% Ti doped PbTe as a high temperature segment has a potential to enhance the efficiency by ∼14% compared to the undoped sample.

The MASCOT Radiometer MARA for the Hayabusa 2 Mission

The MASCOT radiometer MARA is a multi-spectral instrument which measures net radiative flux in six wavelength bands. MARA uses thermopile sensors as sensing elements, and the net flux between the instrument and the surface in the $18^{\circ }$ field of view is determined by evaluating the thermoelectric potential between the sensors’ absorbing surface and the thermopile’s cold-junction. MARA houses 4 bandpass channels in the spectral range of 5.5–7, 8–9.5, 9.5–11.5, and 13.5–15.5 μm, as well as one long-pass channel, which is sensitive in the $>3~\upmu \mbox{m}$ range. In addition, one channel is similar to that used by the Hayabusa 2 orbiter thermal mapper, which uses a wavelength range of 8–12 μm. The primary science objective of the MARA instrument it the determination of the target asteroid’s surface brightness temperature, from which surface thermal inertia can be derived. In addition, the spectral bandpass channels will be used to estimate the spectral slope of the surface in the thermal infrared wavelength range. The instrument has been calibrated using a cavity blackbody, and the temperature uncertainty is 1 K in the long pass channel for target temperatures of $>173~\mbox{K}$ . Measurement uncertainty in the spectral bandpasses is 1 K for target temperatures above 273 K.

Anomalous Temperature Dependence of the Band Gap in Black Phosphorus.

Black phosphorus (BP) has gained renewed attention due to its singular anisotropic electronic and optical properties that might be exploited for a wide range of technological applications. In this respect, the thermal properties are particularly important both to predict its room temperature operation and to determine its thermoelectric potential. From this point of view, one of the most spectacular and poorly understood phenomena is indeed the BP temperature-induced band gap opening; when temperature is increased, the fundamental band gap increases instead of decreases. This anomalous thermal dependence has also been observed recently in its monolayer counterpart. In this work, based on ab initio calculations, we present an explanation for this long known and yet not fully explained effect. We show that it arises from a combination of harmonic and lattice thermal expansion contributions, which are in fact highly interwined. We clearly narrow down the mechanisms that cause this gap opening by identifying the peculiar atomic vibrations that drive the anomaly. The final picture we give explains both the BP anomalous band gap opening and the frequency increase with increasing volume (tension effect).

High thermoelectric potential of Bi2Te3 alloyed GeTe-rich phases

In an attempt to reduce our reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of p-type (GeTe)1−x(Bi2Te3)x alloys, with x values of up to 20%. Higher solubility limit of Bi2Te3 in GeTe, than previously reported, was identified around ∼9%, extending the doping potential of GeTe by the Bi2Te3 donor dopant, for an effective compensation of the high inherent hole concentration of GeTe toward thermoelectrically optimal values. Around the solubility limit of 9%, an electronic optimization resulted in an impressive maximal thermoelectric figure of merit, ZT, of ∼1.55 at ∼410 °C, which is one of the highest ever reported for any p-type GeTe-rich alloys. Beyond the solubility limit, a Fermi Level Pinning effect of stabilizing the Seebeck coefficient was observed in the x = 12%–17% range, leading to stabilization of the maximal ZTs over an extended temperature range; an effect that was associated with the potential of the governed highly symmetric Ge8Bi2Te11 and Ge4Bi2Te7 phases to create high valence band degeneracy with several bands and multiple hole pockets on the Fermi surface. At this compositional range, co-doping with additional dopants, creating shallow impurity levels (in contrast to the deep lying level created by Bi2Te3), was suggested for further electronic optimization of the thermoelectric properties.

Measurement of Thermoelectric Potential Coupling Coefficient for Sandstone Rock Sample

Excessive water production is one of the main problems that occur during hydrocarbon production. During water injection, the less viscous water which has higher mobility than the reservoir fluid, tends to by-pass the oil. This phenomenon is normally called water fingering. Density difference between denser water and oil makes the water segregate to the bottom of layer, creating water tongue. Uncontrolled excessive water production will reduce oil production potential and increase the cost for water management and treatment. This phenomenon is economical unfavorable. Intelligent well integrated with monitoring systems and inflow control valve (ICV) has been applied in producing hydrocarbon. The excessive flow of water into well can be controlled using ICV. There are various methods and approaches been proposed to control water production. One of them is by measuring the spontaneous potential (SP) using permanent sensor outside the insulated casing. However, thermoelectric (TE) potential could also contribute to the measurement of the SP. The main objective of this experiment is to measure TE potential across sandstone rock sample at four different salinities which are 0.001M, 0.01M, 0.1M, and 1.0M of brine (NaCl). The core samples dimension is 7.62 cm in length and 3.81 cm in diameter. Temperature difference up to 80°C was applied to rock sample inducing different TE potentials at different salinities. Gradual heating technique was applied in creating temperature difference by using a temperature controller. Three different experiments were conducted for each salinity and real-time voltage (V) and temperature (T) were recorded using data acquisition system. Then the TE coupling coefficient can be determined by calculating the slope after plotting Voltage versus Temperature Difference. The result is as the salinity increases, TE coupling coefficient decrease and drop to zero around 0.1M. The result shows small but still measurable thermoelectric coupling coefficients.

Band Degeneracy, Low Thermal Conductivity, and High Thermoelectric Figure of Merit in SnTe–CaTe Alloys

Pure lead-free SnTe has limited thermoelectric potentials because of the low Seebeck coefficients and the relatively large thermal conductivity. In this study, we provide experimental evidence and theoretical understanding that alloying SnTe with Ca greatly improves the transport properties leading to ZT of 1.35 at 873 K, the highest ZT value so far reported for singly doped SnTe materials. The introduction of Ca (0–9%) in SnTe induces multiple effects: (1) Ca replaces Sn and reduces the hole concentration due to Sn vacancies, (2) the energy gap increases, limiting the bipolar transport, (3) several bands with larger effective masses become active in transport, and (4) the lattice thermal conductivity is reduced by about 70% due to the contribution of concomitant scattering terms associated with the alloy disorder and the presence of nanoscale precipitates. An efficiency of ∼10% (for ΔT = 400 K) was predicted for high-temperature thermoelectric power generation using SnTe-based p- and n-type materials.

Functional Graded Germanium–Lead Chalcogenide‐Based Thermoelectric Module for Renewable Energy Applications

High thermoelectric conversion efficiencies can be achieved by making use of materials with, as high as possible, figure of merit, ZT, values. Moreover, even higher performance is possible with appropriate geometrical optimization including the use of functionally graded materials (FGM) technology. Here, an advanced n‐type functionally graded thermoelectric material based on a phase‐separated (PbSn0.05Te)0.92(PbS)0.08 matrix is reported. For assessment of the thermoelectric potential of this material, combined with the previously reported p‐type Ge0.87Pb0.13Te showing a remarkable dimensionless figure of merit of 2.2, a finite‐element thermoelectric model is developed. The results predict, for the investigated thermoelectric couple, a very impressive thermoelectric efficiency of 14%, which is more than 20% higher than previously reported values for operating under cold and hot junction temperatures of 50 °C and 500 °C, respectively. Validation of the model prediction is done by a thermoelectric couple fabricated according to the model's geometrical optimization conditions, showing a good agreement to the theoretically calculated results, hence approaching a higher technology readiness level.

Theoretical and experimental investigations of the thermoelectric properties of Bi2S3

Electronic and transport properties of Bi2S3 with various dopants are studied using density functional theory and experimental characterizations. First, principle calculations of thermoelectric properties are used to evaluate the thermoelectric potential of the orthorhombic Bi2S3 structure. The computational screening of extrinsic defects is used to select the most favorable n-type dopants. Among all the dopants considered, hafnium and chlorine are identified as prospective dopants, whereas, e.g., germanium is found to be unfavorable. This is confirmed by experiment. Seebeck coefficient (S) and electrical conductivity (σ) measurements are performed at room temperature on pellets obtained by spark plasma sintering. An increase of power factors (S2·σ) from around 50 up to 500 μW K−2 m−1 is observed for differently doped compounds. In several series of samples, we observed an optimum of power factor above 500 μW K−2 m−1 at room temperature for a chlorine equivalence of 0.25 mol. % BiCl3. The obtained results are plotted on a semilogarithmic log (σ) versus S graph to demonstrate that a very strong linear trend that limits the power factor around 500 μW K−2 m−1 exists. Further improvement of Bi2S3 as thermoelectric material will require finding new doping modes that will break through the observed trend. The results of stability tests demonstrate that properties of optimally doped Bi2S3 are stable.

Prediction of high thermoelectric potential in AMN2 layered nitrides: electronic structure, phonons, and anharmonic effects

Band structures, electronic transport coefficients, harmonic and anharmonic vibrational properties of novel layered nitrides have been studied to evaluate the potential for thermoelectric applications.

Structural, magnetic and transport properties of 2D structured perovskite oxychalcogenides

We have been looking for new potential thermoelectric materials in the family of 2D structured perovskite oxychalcogenides containing [Cu2Ch2]2− blocks (Ch = S or Se). Using high temperature syntheses, a new oxyselenide Sr2CuFeO3Se has been isolated and its structure has been compared to the isotypes sulfides, Ca2CuFeO3S and Sr2CuFeO3S, prepared by the same technique. By combining powder XRD and TEM analyses their composition and structure were analyzed. They all three crystallize in the Sr2CuGaO3S-type structure, with only the oxyselenide showing a Fe deficiency which is related to the stacking faults evidenced by high resolution TEM. Transport and magnetic properties of the samples have been studied; especially their electrical resistivity is characterized by high values in the range from 1 to 10 kΩ cm at 300 K. Thermoelectric potential of these materials is also discussed.

Thermoelectric Properties of Light-Element-Containing Zintl Compounds CaZn2−x Cu x P2 and CaMnZn1−x Cu x P2 (x = 0.0–0.2)

Light-element-containing CaAl2Si2-type Zintl phases CaZn2−xCuxP2 and CaMnZn1−xCuxP2 (x = 0.0–0.2) have been synthesized by solid-state reaction. Electrical resistivity (ρ), Seebeck coefficient (α), and thermal conductivity (κ) were measured over a wide temperature (T) range (80–1000 K) to evaluate the thermoelectric potential of these materials. Below 300 K, the power factor (PF; α2/ρ) is very small. Above 600 K, however, PF increases rapidly for all compositions because of a rapid increase of α and a simultaneous decrease of ρ. The measured large α is consistent with the wider band gap expected for these compositions. Compared with the pure compounds, larger PF values are observed for the Cu-substituted compounds; the largest observed PF is ∼0.5 mW/m K2. The thermal conductivity is found to be rather low, despite the presence of light elements, and is in the range 1.0–1.5 W/m K at 1000 K. Because of the combination of low κ and moderate PF values, the dimensionless figure of merit ZT = α2T/ρκ reaches a maximum of 0.4 for CaZn1.9Cu0.1P2.

Thermoelectric Potential of Polymer-Scaffolded Ionic Liquid Membranes

Organic thin films have been viewed as potential thermoelectric (TE) materials, given their ease of fabrication, flexibility, cost effectiveness, and low thermal conductivity. However, their intrinsically low electrical conductivity is a main drawback which results in a relatively lower TE figure of merit for polymer-based TE materials than for inorganic materials. In this paper, a technique to enhance the ion transport properties of polymers through the introduction of ionic liquids is presented. The polymer is in the form of a nanofiber scaffold produced using the electrospinning technique. These fibers were then soaked in different ionic liquids based on substituted imidazolium such as 1-ethyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium bromide. This method was applied to electrospun polyacrylonitrile and a mixture of polyvinyl alcohol and chitosan polymers. The ion transport properties of the membranes have been observed to increase with increasing concentration of ionic liquid, with maximum electrical conductivity of 1.20 × 10−1 S/cm measured at room temperature. Interestingly, the maximum electrical conductivity value surpassed the value of pure ionic liquids. These results indicate that it is possible to significantly improve the electrical conductivity of a polymer membrane through a simple and cost-effective method. This may in turn boost the TE figures of merit of polymer materials, which are well known to be considerably lower than those of inorganic materials. Results in terms of the Seebeck coefficient of the membranes are also presented in this paper to provide an overall representation of the TE potential of the polymer-scaffolded ionic liquid membranes.

Design of Digital K-Type Thermocouple Temperature Transmitter

The paper introduces a method of digital K-type thermocouple temperature transmitter design, which uses MAX6675, a digital K-type thermocouple converter, MCU and TTL/485 conversion circuit. MCU calculates thermoelectric potential of thermocouple by the result of MAX6675 firstly, and then obtains the temperature by reference tables of K-type thermocouple and linear interpolation method, and result is serial output in digital mode. The method can eliminate interference of analog signal transmission, and improve measurement accuracy.

Effects of Cation Site Substitutions on the Thermoelectric Performance of Layered SnBi2Te4 utilizing the Triel Elements Ga, In, and Tl

AbstractA thorough study on the thermoelectric potential of the layered compound SnBi2Te4 is presented. Phase range studies on SnBi2Te4, unit cell parameters by powder X‐ray diffraction, and electronic structure calculations (both LDA and GGA functional) were performed. Physical property measurements regarding substitution of tin and bismuth with the triel (Tr = Ga, In, Tl) elements are presented towards the improvement of thermoelectric properties, according to TrxSn1–xBi2Te4 and TrxSnBi2–xTe4. The range of inclusion was generally over 0.01 ≤ x ≤ 0.15 to monitor compound changes as well as phase purity limits. Seebeck coefficient, S, electrical conductivity, σ, and thermal conductivity, κ, were measured, yielding the dimensionless Figure of merit, ZT, data over a temperature range between 300 K and 680 K. Results of partial replacements of tin and bismuth are compared and reported. ZTmax values range from 0.10 to 0.34 depending on the dopant, achieved at temperatures from 355 K to 420 K.

Rapid High-Precision Non-Linear Calibration for Temperature Sensors in Transient Aerodynamic Heating Simulation Systems

In order to accurately simulate the transient aerodynamic heating conditions experienced by aircraft when flying at high speeds, rapid and highly precise non-linear dynamic control of the heating process in aerodynamic simulation experiments must be conducted using a transient heat flux control system. This process involves carrying out ‘thermoelectric potential - temperature (E-T)’ conversion of sensors. Here a fast and high-precision ‘E-T’ sensor conversion method for the transient aerodynamic heating control systems of high-speed aircraft is proposed. The developed method has the advantages of easy calculation, rapid conversion speed and high calibration precision, and can thus be employed for fast non-linear dynamic control of rapidly-changing temperature fields in the aerodynamic heating process of high-speed aircraft.