Thermoelectric Properties Measurements

Rectangular shape samples with typical sizes of 10 mm x 4 mm x 1.5 mm were employed to simultaneously measure electrical conductivity o and Seebeck coefficient S by the standard four-probe methods in a He atmosphere (ULVAC-RIKO ZEM-3). Thermal conductivity k was calculated using the equation k = apC from the thermal diflfusivity a obtained by a flash diflusivity method (LFA 457, Netzsch) on a round disk sample with diameter of about 13 mm and thickness of 2 mm, and specific heat Cp was determined by a differential scanning calorimeter method (DSC Q2000, Netzsch). 

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The effective mass of the electrons changes due to lattice strain, alloy additions, radiation damage, phase transformation, and phase content, directly relates to the ability to use electronic property measurements to assess microstructure phase stability. Electronic properties, such as thermoelectric power coefficients, resistivity and induced resistivity measurements, have a demonstrated correlation to solute and phase content, potential phase transformations, as well as residual strain. 

In the field of nonmetallic catalysts, particularly of oxides, Hauffe and co-workers (14a) used only semiconductors for which information concerning electronic and ion defects was available from measurements of electrical conductivity, thermoelectric properties, and Hall effect. These workers obtain a quantitative correlation between the reaction rate, the amount of chemisorption, and the number of electron defects of the catalysts. Since every catalyzed reaction is initiated by a chemisorption process involving one or several of the reacting gases, and because the nature of this chemisorption process determines the subsequent steps of the reaction, it seems appropriate to begin with a discussion of the mechanism of chemisorption. 

Terry M. Tritt and R. T. Littleton, IV, Thermoelectric Properties of the Transition Metal Pentatellurides Potential Low-Temperature Thermoelectric Materials Franz Freibert, Timothy W. Darling, Albert Miglori, and Stuart A. Trugman, Thermomagnetic Effects and Measurements... 

The definition of inhomogeneous thermoelectric properties and the measurement techniques of FGM element also include several technological problems to be solved. 

The thermoelectric properties were measured at room temperature along the direction perpendicular to the pressing direction. The samples with dimensions of 2 X 2 X15 mm and of 4x4x4 mm were cut out of the compound for the measurements of Seebeck coefficient a and thermal conductivity k and of the electrical resistivity p, respectively. Then, their surfaces were polished with a series of SiC polishing papers of up to 2000 and further polished on a polishing cloth impregnated with AI2O3 powders of 0.3 //m size. 

The thermoelectric properties were measured at 300 K for the FGM and its component layers separated from the FGM. The electrical conductivity ((T) and Hall coefficient (Rjj) were measured by the 6-probe method for the FGM and by the van der Pauw configuration for the components cut from the FGM using Pt-wire electrodes. The carrier concentration (n) and Hall mobility (/ h) calculated using the equation n=lleR (e electric charge) and / H= h respectively. The thermoelectric power (a) at 300 K was estimated from the linear relationship between thermoelectromotive force (EMF) and temperature difference within 5 K. 

The thermoelectric properties of the FGM and its components were measured in Ar atmosphere in the temperature region from 300 to 700 K. The sample size was 3 X 3 X 8 mm. On the thermoelectric power measurement, the components of high and low carrier... 

In the previous paper, it was reported that the thermoelectric properties of SiC/B C system could be controlled by the addition of PSS at room temperature. In this report, the porous structure of these samples were confirmed by using SEM, and the measurements were carried out on the temperature dependence of the thermoelectric properties from room temperature up to 600 C (the thermal conductivity up to 300 5C). TTic figure of merit of the sample (B C 2.0 wt.% + PSS 5.0 wt. %) is estimated about 2x10" K around 600 C. 

The measurement of thermoelectric properties employed the DC method with high speed and high resolution[2] to remove fully errors occurring by Peltier effect. The thermo-electromotive force o was measured as a function of temperature difference AT at both ends of a specimen. The thermoelectric power a was obtained from a slope of o-A Tcurve and expressed as an absolute value. 

Fabrication of a thermocouple [34] requires some skill and familiarity, especially when using small-diameter wires. The measuring junction should be a joint of good thermal and electrical contacts produced without destroying the thermoelectric properties of the wires at the junction. For applications below 500°C, silver solder with borax flux is sufficient for most base metal types, whereas junctions formed by welding are recommended for use above... 

A third emf is produced if there is a temperature gradient along either of the materials. The emf generated by the Peltier effect at the junction can be used to measure temperature, knowing the thermoelectric properties of the metals. 

Concentration/separation of sample solutes is one of most important functions in micro- and nanofluidic systems. TGF has proved to be a promising technique that can achieve concentration and separation in microfiuidic devices. However, so far very limited experimental and theoretical investigations have been reported. Experimentally, it is highly desirable to develop various microfiuidic structures that can be utilized by the TGF technique to cmicentrate different samples. Furthermore, more experiments should be carried out to characterize the thermoelectrical properties of buffers and samples so as to obtain the temperature-dependent electroosmotic mobility and electrophoretic mobility, as well as buffer conductivity, viscosity, and dielectric permittivity for each individual sample and buffer solution. In addition, the development of reliable, accurate, high-resolution, experimental techniques for measuring fiow, temperature, and sample solute concentration fields in microfiuidic channels is needed. Theoretically, the model development of TGF is still in its infancy. The models presented in this study assume the dilute solute sample and linear mass flux-driving forces correlations. However, when the concentrations of the sample solute and the buffer solution are comparable, the aforementioned assumptions break down. Moreover, the channel wall zeta potential in this situation may become nonconstant. More comprehensive models should be developed to incorporate the solute-buffer and solute-channel wall... 

A small Curie term has been observed in all metallic conducting polymers at very low temperatures (T < 20 K) [18]. This indicates the presence of localised spins due to impurities, defects, etc. The x T) of PANI-CSA samples near the M-I transition show this behaviour [50]. The density of states at the Fermi level for metallic PANI-CSA and PPy-PFg samples are one states per eV per two rings and three states per eV per four rings, respectively [51]. These values are rather similar to that obtained from the thermoelectric power measurements. The Curie term at low temperatures is lower for metallic samples than for insulating samples. The magnetic properties and spin dynamics in doped conducting polymers are described in recent review articles [51]. 

Although transport property measurements, like thermoelectric power, specific heat, etc., are important in the critical and insulating regimes, they are not as sensitive as the low temperature conductivity and MR. The linear temperature dependence of thermoelectric power and a linear term in the specific heat (which are typical for metallic systems) have been observed in the insulating regime too. As the system moves into the insulating side the hopping contribution to thermoelectric power (5 dominates over the metallic... 

To date, BagAlxSi46-x type-I clathrate samples have been aluminum deficient (Si rich), n-type, and exhibit metallic conductivity. High-temperature thermoelectric properties were measured on BagAlxSi46-x with x = 16 synthesized by direct methods the high temperature zT is promising, with a value of 0.35 for the... 

The circuits schematized below show two possible utilizations of the Seebeck effect, one (left) in closed circuit (and therefore with a potential difference equal to zero) producing a current from thermal energy and the other (right) in open circuit, therefore in the absence of current, called thermocouple and used for measuring temperature differences. These circuits are both made up of two soldered joints of two materials having distinct thermoelectric properties. Case study J8 is devoted to the description and modeling of the thermocouple, also called thermoelectric junction, which is recalled here for comparison. 

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