Seebeck Coefficient Measurements Research Articles

Simulation of polycrystalline bismuth films Seebeck coefficient based on experimental texture identification

Seebeck coefficient values measured for textured polycrystalline Bi films have been compared with numerically computed ones. The proposed computation procedure requires crystallographic texture mapping and values of single-crystalline transport coefficients as input data. The comparison of computed and measured Seebeck coefficients allowed determining the factors affecting films' transport properties except of crystalline texture. Two particular cases are considered: when the film properties are affected only by texture and when they depend on texture and grain size simultaneously.

Thermoelectric properties of YbCd2Sb2 doped by Mg

p-type YbCd2-xMgxSb2 (x = 0.1, 0.2, 0.4, 0.6, 0.8) Zintl phases have been synthesized via melting reaction followed by suitable cooling, annealing, grinding, and spark plasma sintering (SPS) densification processes. The effects of isoelectronic substitution of Mg for Cd on thermoelectric properties have been investigated. Electrical conductivity, Seebeck coefficient, and thermal conductivity measurements have been performed as a function of temperature from 300 to 650 K. The XRD patterns show that the solubility limit x of Mg in the YbCd2-xMgxSb2 is less than 0.8. With increasing Mg content x, the cell parameters a and c of the YbCd2-xMgxSb2 compounds decrease. The isoelectronic substitution of Mg for Cd leads to a remarkable decrease in total thermal conductivity and an increase in Seebeck coefficient, though a slightly decease in electrical conductivity. As a result, the maximum dimensionless figure of merit ZT of 1.08 is obtained at 650 K for YbCd1.9Mg0.1Sb2. Compared with the ZT of 0.78 at 650 K in the unsubstituted YbCd2Sb2, it is improved greatly by 38%.

Measurement of the thermoelectric power factor of films over the 10-400 K range.

The design and development of a novel apparatus for the simultaneous measurement of electrical resistivity and Seebeck coefficient of films is reported here. Mounting stage is integrated inside a cryostat chamber enabling measurements over the 10-400 K temperature range, intended for organic thermoelectrics. Finite element method was used to analyze the thermo-mechanical response of the sample holder. The apparatus was validated against high purity nickel film, and a very good agreement was found.

P-Type highly conductive and transparent NdF3-doped tin oxide films prepared by dip coating

Transparent p-type conducting oxide (TCO) films with high conductivity and transparency are in great need to couple with n-type TCO for various electro-optical devices. The purpose of the current study is to explore p-type TCO films with low electrical resistivity and high optical transmittance. We prepared NdF3-added SnO2 (NFTO) thin films, with 0 to 5mol% NdF3, on a glass substrate by sol–gel dip-coating and post-annealed at 475°C. Structural, optical and electrical properties of the resultant NFTO films were investigated. X-ray diffraction patterns indicate tetragonal rutile SnO2 structure with a preferred (110) orientation for all studied films. The absence of impurity peaks indicates that Nd and F atoms may completely dissolve in SnO2 lattice. All films showed excellent transmittance of 84.7 to 90.6% at a wavelength of 550nm. Optical band gap of the NFTO films reduces from 3.94eV for un-doped film to a minimum of 3.75eV for the film with 4mol% NdF3. We confirmed p-type conduction of NFTO films using both Hall-effect and Seebeck coefficient measurements. The film with 2mol% NdF3 shows the lowest electrical resistivity, 8.2×10−3Ωcm, the highest hole-concentration, 8.96×1019cm−3 and a Hall mobility of 9.74cm2V−1s−1. The developed p-type NdF3 added SnO2 TCO films can couple with n-type SnO2 TCO for homo-junctions, which will lead to wide applications in optoelectronics.

Synthesis, Structure, and Basic Magnetic and Thermoelectric Properties of the Light Lanthanide Aurobismuthides.

We report the crystal structures and elementary properties of the new aurobismuthides La3Au3Bi4, Ce3Au3Bi4, Pr3Au3Bi4, Nd3Au3Bi4, Sm3Au3Bi4, and Gd3Au3Bi4. These ternary compounds are found only for the large lanthanides and crystallize in the cubic Y3Au3Sb4 structure type, which is a stuffed Th3P4-type derivative. The compounds are electron-precise, leading to semiconducting behavior, and display magnetic properties arising from localized lanthanide f states. Resistivity data, Seebeck coefficient measurements, and electronic structure calculations suggest that these phases are heavily doped, p-type semiconductors. Nd3Au3Bi4 and Sm3Au3Bi4 have Seebeck coefficients of 105 and 190 μV/K at 350 K, respectively, making them worthy of further thermoelectric studies.

Low thermal conductivity and improved thermoelectric performance of nanocrystalline silicon germanium films by sputtering

SixGe1−x alloys are well-known thermoelectric materials with a high figure of merit at high temperatures. In this work, metal-induced crystallization (MIC) has been used to grow Si0.8Ge0.2 films that present improved thermoelectric performance (zT = 5.6 × 10−4 at room temperature)—according to previously reported values on films—with a relatively large power factor (σ · S2 = 16 μW · m−1 · K−2). More importantly, a reduction in the thermal conductivity at room temperature (κ = 1.13 ± 0.12 W · m−1 · K−1) compared to other Si–Ge films (∼3 W · m−1 · K−1) has been found. Whereas the usual crystallization of amorphous SiGe (a-SiGe) is achieved at high temperatures and for long times, which triggers dopant loss, MIC reduces the crystallization temperature and the heating time. The associated dopant loss is thus avoided, resulting in a nanostructuration of the film. Using this method, we obtained Si0.8Ge0.2 films (grown by DC plasma sputtering) with appropriate compositional and structural properties. Different thermal treatments were tested in situ (by heating the sample inside the deposition chamber) and ex situ (annealed in an external furnace with controlled conditions). From the studies of the films by: x-ray diffraction (XRD), synchrotron radiation grazing incidence x-ray diffraction (SR-GIXRD), micro Raman, scanning electron microscopy (SEM), x-ray photoemission spectroscopy (XPS), Hall effect, Seebeck coefficient, electrical and thermal conductivity measurements, we observed that the in situ films at 500 °C presented the best zT values with no gold contamination.

Thermoelectric Properties of Tl-Doped SnSe: A Hint of Phononic Structure

Polycrystalline samples with composition Sn1−xTlxSe (for x = 0 to 0.04) have been synthesized from elements of 5 N purity at elevated temperatures. The phase purity of the products was verified by x-ray diffraction analysis. Samples for measurement of transport properties were prepared by hot pressing. The samples were then characterized by measurement of electrical conductivity, Hall coefficient, Seebeck coefficient, and thermal conductivity over the temperature range from 300 K to 725 K. All samples demonstrated p-type conductivity. Tl markedly enhanced the carrier concentration. We discuss the influence of Tl substitution on the free carrier concentration and thermoelectric performance. Investigation of the thermoelectric properties showed an order-of-magnitude improvement, with ZT reaching 0.6 at 725 K. We discuss the distinctive nature of the thermal conductivity of SnSe.

Large anisotropic thermal transport properties observed in bulk single crystal black phosphorus

The anisotropy of thermal transport properties for bulk black phosphorus (BP) single crystal, which might be of particular interest in the fabrication of thermoelectric/optoelectronic devices, was investigated by using angular dependent thermal conductivity and Seebeck coefficient measurements at various temperatures. We found that the maximum thermal conductivities in x (zigzag), y (armchair), and z (perpendicular to the puckered layers) directions are 34, 17, and 5 W m−1 K−1, respectively, exhibiting large anisotropy. At temperature around 200 K, a large Seebeck coefficient up to +487 ± 10 μV/K has been obtained in x direction, which is 1.5 times higher than that in z direction. The large anisotropy of thermal transport properties can be understood from the crystal structure and bonding characters of BP. In addition, the energy gap has been obtained from nuclear spin lattice relaxation measurements, which is consistent with the value derived from temperature-dependent Seebeck coefficient measurements.

Correlations between Structural and Electronic Properties in the Filled Skutterudite Smy(FexNi1-x)4Sb12.

A structural study of the filled skutterudite Smy(FexNi1-x)4Sb12 was performed by means of X-ray powder diffraction and μ-Raman spectroscopy with the aim to unveil the correlations between structural and electronic properties of this material and to favor the improvement of its thermoelectric performance. Samples were prepared by direct reaction of the elements at 1223 K, followed by quenching and subsequent sintering at 873 K; microstructure and composition of the obtained products were determined by SEM-EDS. The position of the boundary separating regions that obey hole- and electron-based conduction mechanisms was found by X-ray diffraction at x ≈ 0.63 and y ≈ 0.30, confirmed by measurements of room-temperature Seebeck coefficient, and discussed on the basis of crystallographic data. The presence of a discontinuity is observed in several structural and spectroscopic parameters at the p/n crossover; it is interpreted as associated with the change in the conduction mechanism. The role of the rare earth filling fraction in driving the structural response of the material is investigated too. The advantage of using X-ray diffraction and μ-Raman spectroscopy as aids in the study of electronic properties of this material is highlighted, as well as the complementarity of the two techniques.

Augmentation of thermoelectric performance of VO2 thin films irradiated by 200MeV Ag9+-ions

Abstract Swift Heavy Ion (SHI) irradiation with 200 MeV Ag9+-ion beam at ion fluences of 1E11, 5E11, 1E12, and 5E12 for tuning of electrical transport properties of VO2 thin films fabricated by so–gel technique on alumina substrates has been demonstrated in the present paper. The point defects created by SHI irradiation modulate metal to insulator phase transition temperature, carrier concentration, carrier mobility, electrical conductivity, and Seebeck coefficient of VO2 thin films. The structural properties of the films were characterized by XRD and Raman spectroscopy and crystallite size was found to decrease upon irradiation. The atomic force microscopy revealed that the surface roughness of specimens first decreased and then increased with increasing fluence. Both resistance as well as Seebeck coefficient measurements demonstrated that all the samples exhibit metal–insulator phase transition and the transition temperatures decreases with increasing fluence. Hall effect measurements exhibited that carrier concentration increased continuously with increasing fluence which resulted in an increase of electrical conductivity by several orders of magnitude in the insulating phase. Seebeck coefficient in insulating phase remained almost constant in spite of an increase in the electrical conductivity by several orders of magnitude making SHI irradiation an alternative stratagem for augmentation of thermoelectric performance of the materials. The carrier mobility at room temperature decreased up to the beam fluence of 5E11 and then started increasing whereas Seebeck coefficient in metallic state first increased with increasing ion beam fluence up to 5E11 and thereafter decreased. Variation of these electrical transport parameters has been explained in detail.

Determining a hopping polaron's bandwidth from its Seebeck coefficient: Measuring the disorder energy of a non-crystalline semiconductor

Charge carriers that execute multi-phonon hopping generally interact strongly enough with phonons to form polarons. A polaron's sluggish motion is linked to slowly shifting atomic displacements that severely reduce the intrinsic width of its transport band. Here a means to estimate hopping polarons' bandwidths from Seebeck-coefficient measurements is described. The magnitudes of semiconductors' Seebeck coefficients are usually quite large (>k/|q| = 86 μV/K) near room temperature. However, in accord with the third law of thermodynamics, Seebeck coefficients must vanish at absolute zero. Here, the transition of the Seebeck coefficient of hopping polarons to its low-temperature regime is investigated. The temperature and sharpness of this transition depend on the concentration of carriers and on the width of their transport band. This feature provides a means of estimating the width of a polaron's transport band. Since the intrinsic broadening of polaron bands is very small, less than the characteristic phonon energy, the net widths of polaron transport bands in disordered semiconductors approach the energetic disorder experienced by their hopping carriers, their disorder energy.

超格子構造 DLC 膜の熱電特性評価

This paper presents an investigation of the thermoelectric performance of super lattice structure diamond-like carbon (DLC) Films deposited on glass substrates using unbalanced magnetron sputtering (UBMS). It was measured Seebeck coefficient and resistivity of the DLC film. Then, to evaluate its thermoelectric performance. The super lattice structure DLC films showed a Seebeck effect, and they had p-type semiconductor characteristic. The super lattice structure DLC than a W doped DLC single layer film is the Seebeck coefficient is increased. The superlattice structure DLC than a W doped DLC single layer film is the specific resistance is increased. Power factor (PF) of the superlattice of the DLC film was lower than the W doped DLC single layer. Results show that the PF quality of superlattice structure DLC films was affected strongly by the magnitude of the specific resistance.

ガリウム添加ZnO薄膜の構造・熱電特性の実験および理論的特性評価

We performed experimental and theoretical investigations of structural and thermoelectric properties of Ga-doped ZnO thin films. We prepared the thin films by a RF magnetron sputtering with various argon gas pressures, followed by thermal annealing at 500°C for 60 min in vacuum condition. We evaluated surface morphology and crystallographic properties as the structural properties of the ZnO thin films. To estimate the thermoelectric properties, we performed Hall measurement and the measurements of electrical conductivity, Seebeck coefficient and power factor. For theoretical analysis, we estimated an energy band structure of ZnO by first-principle calculation (ABINIT) based on density function theory with local density approximation, followed by the calculation of transport properties by BoltzTraP code. As a result, we found that the thin films at 2.0 Pa obtained the highest power factor of 0.73 µW/(cm･K²). Even though the transport properties were exhibited certain differences between the experimental results and the theoretical results, we observed the approximate trend of the transport propeties of ZnO.

Apparatus for the measurement of electrical resistivity, Seebeck coefficient, and thermal conductivity of thermoelectric materials between 300 K and 12 K.

We have developed a custom apparatus for the consecutive measurement of the electrical resistivity, the Seebeck coefficient, and the thermal conductivity of materials between 300 K and 12 K. These three transport properties provide for a basic understanding of the thermal and electrical properties of materials. They are of fundamental importance in identifying and optimizing new materials for thermoelectric applications. Thermoelectric applications include waste heat recovery for automobile engines and industrial power generators, solid-state refrigeration, and remote power generation for sensors and space probes. The electrical resistivity is measured using a four-probe bipolar technique, the Seebeck coefficient is measured using the quasi-steady-state condition of the differential method in a 2-probe arrangement, and the thermal conductivity is measured using a longitudinal, multiple gradient steady-state technique. We describe the instrumentation and the measurement uncertainty associated with each transport property, each of which is presented with representative measurement comparisons using round robin samples and/or certified reference materials. Transport properties data from this apparatus have supported the identification, development, and phenomenological understanding of novel thermoelectric materials.

Improved thermoelectric properties in heavily doped FeGa3

FeGa3, a hybridization gap semiconductor, has been substituted with an n-type dopant Ge to form a series of compositions FeGa3−xGex. Electrical and thermal transport properties of these compositions have been studied. Change in carrier density (n) is evident from the Hall measurements. The carrier density (n) can be as high as ∼1021 cm−3 in these compositions. In order to study the role of heavy doping on the thermoelectric properties of FeGa3, an alloy series Fe1−yCoyGa3−xGex has also been synthesized with higher concentrations of Ge (x = 0.1–0.35) and Co (y = 0.1–0.5). From resistivity and Seebeck coefficient measurements, it appears that heavy doping is accomplished by the simultaneous substitutions of Ge and Co. The systematic change in both resistivity (ρ) and Seebeck coefficient (α) is possibly due to change in the carrier density (n). The power factor (PF) α2/ρ improves steadily with increasing carrier density and the best PF ∼1.1 mW/m K2 is observed for the heavily doped compositions at 875 K. In the alloy series Fe1−yCoyGa3−xGex, thermal conductivity is also reduced substantially due to point defect scattering. Due to higher power factors, the figure of merit ZT improves to 0.25 at 875 K for the heavily doped compositions.

Hall and Seebeck measurements estimate the thickness of a (buried) carrier system: Identifying interface electrons in In-doped SnO2 films

We propose a simple method based on the combination of Hall and Seebeck measurements to estimate the thickness of a carrier system within a semiconductor film. As an example, this method can distinguish “bulk” carriers, with homogeneous depth distribution, from “sheet” carriers, that are accumulated within a thin layer. The thickness of the carrier system is calculated as the ratio of the integral sheet carrier concentration, extracted from Hall measurements, to the volume carrier concentration, derived from the measured Seebeck coefficient of the same sample. For rutile SnO2, the necessary relation of Seebeck coefficient to volume electron concentration in the range of 3 × 1017 to 3 × 1020 cm−3 has been experimentally obtained from a set of single crystalline thin films doped with varying Sb-doping concentrations and unintentionally doped bulk samples, and is given as a “calibration curve.” Using this calibration curve, our method demonstrates the presence of interface electrons in homogeneously deep-acceptor (In) doped SnO2 films on sapphire substrates.

Anisotropic transport properties of tungsten disulfide

Single crystals of WS2 were prepared by chemical vapor transport method using sulfur as a transport agent. Measurements of electrical resistivity, Seebeck coefficient and thermal conductivity as a function of temperature, along the in-plane and the out-of-plane directions reveal distinct trends. In our interpretation these differences are mainly due to the different nature of the chemical bonding in the two directions and to the presence of impurity intercalates in between the planes.

Evaluation of W-containing Sr1 −xBaxFe0.75W0.25O3–δ (x = 0, 0.5, 1) anode materials for solid oxide fuel cells

In this work, W-containing Sr1−xBaxFe0.75W0.25O3−δ (x=0, 0.5, 1) perovskite-related oxides have been for the first time evaluated in terms of their possible application as anode materials in solid oxide fuel cells. Crystal structure, thermal expansion coefficient, transport properties, oxygen content, chemical compatibility in relation to ceria-based electrolyte, and stability of the materials in reducing atmospheres have been studied. It was found that SrFe0.75W0.25O3−δ and Sr0.5Ba0.5Fe0.75W0.25O3−δ oxides show simple perovskite-type structure with cubic Pm-3m symmetry, while BaFe0.75W0.25O3−δ exhibits hexagonal P63/mmc structure. Small grains (~2μm) can be obtained for SrFe0.75W0.25O3−δ compound with very simple, high-temperature synthesis process in air. Large oxygen nonstoichiometry changes of Δδ≈0.36 were observed for SrFe0.75W0.25O3−δ oxide upon heating in 5vol.%H2 in argon. Seebeck coefficient and electrical conductivity measurements revealed that SrFe0.75W0.25O3−δ oxide exhibits p-type conductivity in air and n-type conductivity under reducing conditions. This oxide presents relatively good chemical compatibility in relation to Ce0.8Gd0.2O1.9 electrolyte, and chemical stability in 5vol.%H2 in argon up to at least 800°C. Electrochemical impedance spectroscopy studies for SrFe0.75W0.25O3−δ-based cells conducted in pure hydrogen and CH4 indicated the possibility of the application of SrFe0.75W0.25O3−δ as the anode material in SOFCs.

Simultaneous Thermoelectric Property Measurement and Incoherent Phonon Transport in Holey Silicon

Block copolymer patterned holey silicon (HS) was successfully integrated into a microdevice for simultaneous measurements of Seebeck coefficient, electrical conductivity, and thermal conductivity of the same HS microribbon. These fully integrated HS microdevices provided excellent platforms for the systematic investigation of thermoelectric transport properties tailored by the dimensions of the periodic hole array, that is, neck and pitch size, and the doping concentrations. Specifically, thermoelectric transport properties of HS with a neck size in the range of 16-34 nm and a fixed pitch size of 60 nm were characterized, and a clear neck size dependency was shown in the doping range of 3.1 × 10(18) to 6.5 × 10(19) cm(-3). At 300 K, thermal conductivity as low as 1.8 ± 0.2 W/mK was found in HS with a neck size of 16 nm, while optimized zT values were shown in HS with a neck size of 24 nm. The controllable effects of holey array dimensions and doping concentrations on HS thermoelectric performance could aid in improving the understanding of the phonon scattering process in a holey structure and also in facilitating the development of silicon-based thermoelectric devices.

Synthesis and Thermoelectric Properties of the YbTe-YbSb System

The syntheses of YbTe1−x Sb x (x = 0, 0.05, 0.2, 0.5, 0.8, 1) were investigated by solid state reactions and formed into dense pellets by spark plasma sintering. X-ray powder diffraction and microprobe analysis indicated no solubility of Sb in YbTe, and these phases are better described as composite phases (YbTe)1−x (YbSb) x (x = 0, 0.05, 0.2, 0.5, 0.8, 1). Thermal conductivity, electrical resistivity, and Seebeck coefficients were acquired for the larger values of x (x = 0.2, 0.5, 0.8, 1) from room temperature to 773 K, and the figure of merit was calculated. Thermal conductivities for x = 0, 0.05 are also reported; however, measurements of Seebeck coefficients and electrical resistivity were not possible due to large resistivity. The figure of merit for all samples was low, and the maximum zT measured was zT 791K = 0.018 for YbSb. Low figures of merit were primarily the result of very high resistivity in YbTe rich samples, and high thermal conductivity, and a small Seebeck coefficient in all samples.