Thermoelectric effect pdf

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Download references. We thank M. Isomura, N. Kojima, B. Masaoka, T. Sasaki, K. Suzuki and B. Varaprasad for their support in sample preparation, and T. Seki and M. Murata for valuable discussions. You can also search for this author in PubMed Google Scholar.

All the authors discussed the results and commented on the manuscript. Correspondence to Ken-ichi Uchida or Yuya Sakuraba. Peer Review information Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. A Peltier module was thermally connected to two Cu blocks. The thermoelectric performance for either power generation or cooling depends on the efficiency of the thermoelectric material for transforming heat into electricity.

Nearly all good thermoelectric materials are heavily doped semiconductors: semiconductors which have so many free electrons that they have many properties similar to metals. The charge carrier concentration depends on intrinsic defects such as atom vacancies as well as extrinsic dopants impurities.

This eliminates the need to re-optimize the charge carrier concentration that is needed but often forgotten when analysing the power factor. A more generalized treatment uses the Boltzmann Transport Function Analysis to understand the properties of Complex Electronic Materials. We normally consider just one charge carrying species at a time, but when there are multiple charge carrying species, such as electrons and holes or electrons in multiple bands , or ions, the total coductivity is the sum of the individual conductivities, combining like resistors in parallel.

For example, if just electrons and holes:. Although resistivity and conductivity are scalar material properties for cubic or isotropic materials, they are tensor properties in general. For most materials orthorhombic symmetry or greater simply making sure to measure all properties along the same direction will usually suffice. Electrical resistivities from different dissipating mechanisms typically add like resistors in series and therefore plotting experimental values as resistivities rather than conductivities is usually more helpful in identifying different scattering mechanisms.

For example in metals or heavily doped semiconductors such as thermoelectric materials the temperature dependent resistivity often follows the approximate form of a straight line. Additional homogeneous scattering mechanisms can be included using Matthiessen's Rule.

Grain boundaries , impurity phases and inhomogeneaities can have profound effects on the measured electrical resistivity but are often ignored as the physical treatment essentially assumes single crystal material.

In the Quantum Mechanics based Boltzmann Transport Theory it is the electron group velocity and density-of-states that determines how electrons transport charge. This makes the classical concepts of mobility and effective mass difficult to precisely define and so we will use experimentally based approaches to define them here.

When there are multiple scattering mechanisms, Mathiessen's rule is typically used. Electron scattering mechanisms are typically identified by their effect on electron mobility.

The mobility and charge carrier concentration are often estimated using Hall Effect measurements. The Hall Mobility is determined from measurements of the Hall Effect and Electrical Resistivity while the Weighted Mobility which gives similar information about charge transport mechanisms can be determined from measurements of the Seebeck Coefficient and Electrical Resistivity [21]. The weighted mobility, easily computed from measurements of the Seebeck coefficient and electrical resistivity can be used like the Hall Mobility to identify charge transport mechanisms by examining the temperature dependence [21].

The scattering rate is an integral part of transport theory. The scattering time of the semi-classical Drude Model is typically equated with the relaxation time of Boltzmann Transport Theory.

The scattering rate of an electron depends on its velocity, the density of scattering centers and their effective area or scattering cross section [23]. This simple description can be used to justify the physical form of the scattering rate. For a metal, the velocity of electrons does not change much with temperature - that can be described by a high Fermi Velocity. In the quantum mechanical description of scattering is easiestly seen using Fermi's Golden Rule.

Here elastic scattering is assumed, where the energy of the electron is unchanged. Deformation of a crystal due to a phonon wave, alters the energy of the conduction and valence bands resulting in the scattering of conducting electrons and holes, known as electron-phonon scattering by a deformation potential [12].

For example, in deformation potential scattering deformation of the crystal changes the energy of electrons which scatters transporting electrons [12]. Although this scattering is often called Acoustic Phonon Scattering , and the above equation is based on such a theory, Phonon scattering in complex thermoelectric materials, which could be dominated by optical phonons, appears to fit the temperature and energy dependence given above.

Most materials, particularly complex thermoelectric materials, are not single phase crystals. They almost always contain grain boundaries, impurity phases and porosity even if only in trace amounts. The effects of such inhomogeneaities is often ignored in physical models which is not a problem when the effects are small as often is the case in thermoelectric materials where defects are oftened screened.

Nevertheless, one should always have an estimate of the approximate volume fraction of phases present and look for common effects of interfaces and grain boundaries on transport properties. Inhomogenaities occur at many length scales are can be easily misidentified. Archimedes density measurement may not detect open porosity. Inhomogeneaities are often at micron or milimeter scale that can be easily missed by TEM microscopy and are better observed with SEM or scanning Seebeck [25].

Nanometer scale inhomogeneaities are best observed in TEM or APT [26] but could actually be artifacts [27, 28] caused by sample preparation or damage during observation. Inhomogeneous material consisting of a random mixture of a Matrix Phase and a Dispersed Phase. The transport properties, such as electrical or thermal conductivity can be estimated using an Effective Medium model requireing only the volume fraction of the dispsersed phase and the properties of each component.

Such a model can also be used for porous materials [23]. The easiest estimate for the effect on a material's transport properties is to use an Effective Medium model for an isotropic material such as the Reynolds and Hough rule for mixtures same as Maxwell Garnett for dielectric constant. Effective Medium models should give results between the ideal case of the materials connected in series or connected in parallel.

Using the magnetic field dependence of the electrical conductivity the properties of the matrix and dispersed phases can be determined [29]. Effective Medium models can also include Interface or grain boundary phases, and effects of anistotropic dispersed phases [30]. Bell, L. Science , — Putley, E. Nagaosa, N. Download references. You can also search for this author in PubMed Google Scholar.

Correspondence to Andrew F. Reprints and Permissions. May, A. Twisting the thermoelectric potential. Download citation. Published : 18 January Issue Date : April Anyone you share the following link with will be able to read this content:.

Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative. The thermoelectric module is a heat pump and has similar function as a refrigerator. It gets along however without mechanically small construction units pump, compressor and without cooling fluids. The heat flow can be turned by reversal of the direction of current.

Thermoelectric cooling provides an alternative solution to the common compressor and absorber cooler. Thermoelectric coolers are used especially if small cooling power is required up to W.

If this system comes in present HVAC system, then revolution will occur in the automobile. With rising population and pollution at an alarming rate this system has come to rescue as these are environment friendly and compact. Conventional compressor run cooling equipment have more limitations related to energy efficiency and Chloro-Fluro Carbon CFC refrigerants use.

Both these factors indirectly point to the impending scenario of global warming. As most of the electricity generation relies on the coal power plants, which add greenhouse gases to the atmosphere is the more cause of global warming. Although researches are going on, best alternatives for the CFC refrigerants is still on the hunt. So instead of using conventional air conditioning systems, other products which can efficiently cool a person are to be planned. By using other efficient cooling device, we can save the electricity bills as well as control the greenhouse gases that are currently released into the surrounding atmosphere.

Although thermoelectric property was discovered about two centuries ago thermoelectric device save only been commercialized during current years. The applications of thermoelectric vary from small refrigerator. In present scenario, hvac system commonly used in the air conditioners is very efficient and reliable but it has some demerits. It uses refrigerants like freon, ammonia, etc. Due to the use of such refrigerants maximum output can be obtained butit leads to much harmful effect to our environment i.

The global warming. That leads to the emergence of finding analternative of the conventional hvac system, i. Thermoelectric cooling and heating system. The present paper deals with thestudy of thermoelectric air conditioner using tec module. Thermoelectric cooling system have advantages over conventionalcooling devices, such as compact size, light in weight, low cost, high reliability, no mechanical moving parts and no working fluids. Air conditioning systems is used in many automobile applications.

The conventional process using refrigerant can cause serious problems to the environment. In this study we developed the air conditioning system based on thermoelectric properties. In this air conditioning, there is no use of compressor and pump for the refrigeration.