Seebeck thermoelectric effect

Seebeck s outstanding scientific achievement was the discovei"y of one of the three classical thermoelectric effects, which are the Seebeck, the Peltier, and the Thomson effects. Seebeck s discovery was the first, dating from 1822—1823, followed by that of Jean-Charles-Athanase Peltier in 1832 and that of William Thomson in 1854. Seebeck obseiwed that an electric current in a closed circuit comprised different metallic components if he heated the junctions of the components to different temperatures. He noted that the effect increases linearly with the applied temperature difference and that it crucially depends on the choice of materials. Seebeck tested most of the available metallic materials for thermoelectricity. His studies were further systematized by the French physicist... 

Thermoelectric effect discovered by T.J. Seebeck The Seebeck effect is the basis for the thermometers designated as thermocouples... 

The thermoelectric effect is due to the gradient in electrochemical potential caused by a temperature gradient in a conducting material. The Seebeck coefficient a is the constant of proportionality between the voltage and the temperature gradient which causes it when there is no current flow, and is defined as (A F/A7) as AT- 0 where A Fis the thermo-emf caused by the temperature gradient AT it is related to the entropy transported per charge carrier (a = — S /e). The Peltier coefficient n is the proportionality constant between the heat flux transported by electrons and the current density a and n are related as a = Tr/T. 

A second historical line which, is of paramount importance to the present understanding of solid state processes is concerned with electronic particles (defects) rather than with atomic particles (defects). Let us therefore sketch briefly the, history of semiconductors [see H. J, Welker (1979)]. Although, the term semiconductor was coined in 1911 [J. KOnigsberger, J, Weiss (1911)], the thermoelectric effect had already been discovered almost one century earlier [T. J. Seebeck (1822)], It was found that PbS and ZnSb exhibited temperature-dependent thermopowers, and from todays state of knowledge use had been made of n-type and p-type semiconductors. Faraday and Hittorf found negative temperature coefficients for the electrical conductivities of AgzS and Se. In 1873, the decrease in the resistance of Se when irradiated by visible light was reported [W. Smith (1873) L. Sale (1873)]. It was also... 

Finally, a very simple molecular electronic component is benzene-1,4-dithiol, which is readily used as a linker between gold electrodes in the same way as the cobalt terpyridine complex shown in Figure 11.40. Benzene dithiol has been used to demonstrate the thermoelectric effect in molecular electronic systems as a linker between a gold surface and the gold tip of a modified atomic force microscope. Thermoelectricity (termed the Seebeck effect) is the generation of an electrical potential... 

In a nonisothermal system, an electric current (flow) may be coupled with a heat flow this effect is known as the thermoelectric effect. There are two reciprocal phenomena of thermoelectricity arising from the interference of heat and electric conductions the first is called the Peltier effect. This effect is known as the evolution or the absorption of heat at junctions of metals resulting from the flow of an electric current. The other is the thermoelectric force resulting from the maintenance of the junctions made of two different metals at different temperatures. This is called the Seebeck effect. Temperature measurements by thermocouples are based on the Seebeck effect. 

This expression shows that the imposition of a temperature difference dT in the absence of any current produces a difference d i in electrochemical potential i.e., d ife) = —z/a, dT. This effect is known as the thermoelectric effect, and the ratio d i/e)/dT, or A(f,/e)/Ar = —ZiCii is known as the Seebeck coefficient (1823), or thermoelectric power.Experimentally, the difference of electrochemical potential may be measured by a voltmeter under open circuit conditions, and dT, measured by means of thermocouples a, is thereby experimentally determined. As defined here for p-type (n-type) material the measured Seebeck coefficient is a positive (negative) quantity. For, and both increase in the direction of increasing hole or electron concentration, which is in a direction opposite to the increase in temperature. Comparison with (6.9.2) shows that Ui = ZiSgfe. Then Eq. (6.9.6) becomes... 

Temperature measurement using thermocouples is based on the thermoelectric effect. Two dissimilar metals are joined together at a junction where an electromotive force (emf) is generated according to the Seebeck effect. The emf level depends on the junction temperature. The Peltier effect causes an emf to be generated when the dissimilar metals are connected to an electrical circuit. 

In the Seebeck or thermoelectric effect a voltage difference arises between two contacts to a semiconductor when they are held at different temperatures. Results are usually expressed in terms of the Seebeck coefficient, the ratio of the voltage difference to the temperature difference. The polarity of the thermoelectric power determines the sign of the majority carrier as the polarity of the cold junction. CompUcations (and incorrect interpretations) may arise if the space charge layers are too thick or the carrier concentration too low. The technique does not distinguish between electronic and ionic conduction. 

Figure 15.12 Thermoelectric effects (a) the Seebeck effect, (h) the Peltier effect and (c) the Thompson effect...

The effectiveness of devices using thermoelectric effects depends on the magnitude of the relative Peltier coefficient, II, or its equivalent, the relative Seebeck coefficient, S. However, these are not the only material parameters of importance. As an example, consider the operation of a heat pump. The amount of heat produced or absorbed is... 

Seebeck, Thomas Johann (1770-1831) was born in Estonia. He showed that a current flowed when you join two metals that are at different temperatures (the thermoelectric effect) this led to the invention of the thermocouple. 

Thermocouple (Fig. 2) is one of the most widely used sensors for temperamre measurement and control. The mechanism underlying the function of thermocouples is the so-called thermoelectric effect or Seebeck effect, named after the German-Estonian physicist Thomas J. Seebeck in 1821. 

Thermoelectric ects occur whenever more than one type of metal is used in the measurement circuit, which includes the sensing element, the leads, and the readout instrumentatimi. The typical Seebeck coefficient between different metals is around 10 pV/K or more, and it is not unusual for temperature to vary by 5—10 °C between different parts of an apparatus even for room-temperature measurements. Thus, thermoelectric effects can be expected to contribute voltages of 100 pV or more if no precautions are taken, which may lead to errors of 1 °C when measuring the RTD temperature around 300 K, and potentially much worse away from 300 K. The first... 

Due to their compactness and standard fabrication technology, the temperature in thermal flow sensors is often measured by thermocouples, which rely on the thermoelectric effect. The thermoelectric effect describes the coupling between the electrical and thermal currents, especially the occurrence of an electrical voltage due to a temperature difference between two material contacts, known as the Seebeck effect. In reverse, an electrical current can produce a heat flux or a cooling of a material contact, known as the Peltier effect. A third effect, the Thomson effect, is also connected with thermoelectricity, where an electric current flowing in a temperature gradient can absorb or release heat from or to the ambient [10, 11]. The relation between the first two effects can be described by methods of irreversible thermodynamics and the linear transport theory of Onsager in vector form. 

The other two thermoelectric effects are the Seebeck effect, Eab(Ti,T2), that gives the emf between the junctions at different temperatures of a circuit out of two different conductors, and the Thomson effect that refers to the reversible heat absorption which occurs when an electric current flows in a homogeneous conductor in which there is a temperature gradient, AQ = o.p (T)(dT/dx)iAt. 

There is currently some interest in P compounds which show thermoelectric effects (Peltier effect or Seebeck effect). Compounds such as Sii (CuP3)j and Gei (CuP3) have been investigated [72]. 

Thermoelectric effects demonstrate the existence of coupling between electrical and thermal phenomena and include the well-known Seebeck effect and Peltier heat, which are explained shortly in the next sections. 

Many thermoelectric effects. The Peltier effect consists of the generation of an entropic flow (heat flow) at passing of a current, whereas the Seebeck effect is the reverse phenomenon, allowing the production of electricity from a difference of temperature. 

Probe Thermometers. Volume expansion thermometers use the expansion of liquids with rising temperature through a narrow tube. The expansion coefficient, defined as the increase in volume per unit volume per unit rise in temperature, is 0.00018 per Kelvin for mercury and 0.00109 per Kelvin for ethyl alcohol colored with dye. Calculating temperature from the actual random thermal motion velocity of every molecule, or the energy contained in a vibrational excitation of every molecule, is impractical. So temperature is measured indirectly in most applications. Different metals expand to different extents when their temperature rises. This difference is used to measure the bending of two strips of metal attached to one another in outdoor thermometers. Thermocouples use the Seebeck or thermoelectric effect discovered by Cerman physicist Thomas Johann Seebeck, in which a voltage difference is produced between two junctions between wires of... 

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