Seebeck coefficient also

The number of mobile holes is equal to the number of impurity Ni2+ ions, and so the fraction c in the Heikes equation is equal to x in LaNi,Coi -,(+. In accord with the theory, the Seebeck coefficient, a, is positive and greatest at low values of x and decreases as x increase (Fig. 1.12). Substituting a value of c = 0.02 into the equation yields a value of a = +335 pV K-1, in good agreement with the experimental value of 360 pV K-1 (Robert el al., 2006). Note that the above example also shows that an experimentally determined value of the Seebeck coefficient can be used to estimate the concentration of impurity defects in a doped oxide. 

The transport properties of the system Fe[V,Fe2-x]04 exhibit a sharp cusp at X == 1.89 and a large, positive Seebeck coefficient correlates well with a small hole concentration on the A sites in the domain 1.89 x < 2.0. The Mossbauer data also support the valency distribution... 

Similar investigations have been carried out for the system LaCr xMnx03 [106]. A significant improvement in sinterability appears when Mn is substituted for Cr. For example, densities above 95% of theoretical were achieved at 1475 °C in air for La0.9Sr0 ]Cr03Mn07O3. Electrical conductivity and Seebeck coefficient results are interpreted by a small polaron mechanism for all compositions. This is illustrated for conductivity in Fig. 33. It was also demonstrated that the carrier (electron hole) mobility rather than carrier concentration governs the electronic transport. 

The Seebeck coefficient gives the amount of voltage generated (in microvolts) by a 1°C change in temperature. The value of the Seeback coefficient varies not only with the thermocouple type but also with temperature. 

The phenomenological equations (6.9.1) have thus been reexpressed in (6.9.9) solely in terms of the measurable transport coefficients a, k, and o. The Seebeck coefficient may be interpreted as the entropy carried per electronic charge. Equation (6.9.9a) represents a further generalization of Ohm s Law, showing how the current density behaves in the presence of a temperature gradient see also Exercise 6.9.3. Equation (6.9.9b) specifies the entropy flux under the joint action of a gradient in electrochemical potential and in temperature this represents a generalization of Fourier s Law. 

By the usage of two staged graded FGM element the FGM effect on thermoelectric performance such as Seebeck coefficient and power factor was investigated. Moreover, the thermoelectromotive force for overaU temperature difference was also evaluated. 

In Equation [7.7], is the Seebeck coefficient of the gas sensitive film, AVgst is the measured thermovoltage of the gas sensitive film, and AT is the temperature difference at the junctions between the gas sensitive layer and the conductor tracks. Due to the fact that the conductor tracks also add a thermovoltage, the thermopower of the gas sensitive layer has to be corrected by the thermopower of the conductor track material (here, platinum), J7p,. 

Yao et at not only measured the TE properties of SWNT/PANI hybrid nanocomposites but also characterized the structure features of PANI molecular chain in the composite [6]. They found that the SWNT/PANI nanocomposites show both higher electrical conductivity and Seebeck coefficient than pure PANI (Figure 6.26). 

It was shown that the Seebeck coefficient of the PEDOT PSS/Te hybrid is significantly larger than that of the pure PEDOT PSS polymer. Besides, electrical conductivity of the hybrid films is also higher than those of both the Te nanorods and PEDOT PSS polymer, indicating that the PEDOT PSS protects the Te from oxidation and improves inter particle contact. By varying the Te content, it was found the electrical conductivity and the TE power factor of the composite exhibit a peak at an intermediate nanowire mass fraction, whereas the Seebeck coefficient increases monotonically with increasing Te, as shown in Figure 6.37 [17]. 

PbTe and PEDOT nanotube composite was also prepared by adding PbTe nanoparticles into a polymerization media [20]. After adding PbTe nanoparticles into the solution, the nanoparticles were adsorbed on the surface of the PEDOT nanotubes at the acetonitrile/n-hexane interface. The electrical conductivity of the composite powders after cold pressing increases with increasing PbTe content while the Seebeck coefficient decreases from 4088 to 1205 pV/K (the composite with 43.9 wt.% PbTe), as shown in Figure 6.39. 

The basic element in a thermopile is a junction between two dissimilar conductors having a large Seebeck coefficient 0. To perform efficiently a large electrical conductivity a is required to minimize Joulean heat loss and a small thermal conductivity K to minimize heat conduction loss between the hot and cold junctions of the thermopile. These requirements are incompatible and we find that in common with other thermoelectric devices (Goldsmid [3.12]) the best choice of thermoelectric material is that for which a0 K is a maximum and that this occurs for certain heavily doped semiconductors, for example BijTcj and related compounds. To make an efficient thermal infrared detector the device must also be an efficient absorber o f the incident radiation and must have a small thermal mass to give as short a response time as possible. 

In Graph 13.13, it can be observed that the Seebeck coefficient is also a nonelementary factor as it can be expressed, when it is a constant, as the ratio of the gas constant (or the Boltzmann constant) on the ionic molar (respectively molecular) charge... 

Like metals and also due to its electrical conductivity, G is a material that also has a high heat transmission capacity. In addition, one of the properties of G directly related to the interplay between heat and electrical conductivity is its high Seebeck coefficient that measures of efficiency to generate voltage when the material is submitted to heating on one side as consequence of the temperature gradient between the two faces. 

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