- This page is about devices that use the thermoelectric effect. For the physics underlying the thermoelectric effect, see thermoelectric effect
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely when a voltage is applied to it, it creates a temperature difference...
.
Thermoelectricity (
thermoThermo, descended from , meaning heat, is a prefix referring to heat or temperature, e.g.,* thermodynamics, the physics of energy, heat, work, and entropy, which is also discussed in the article heat* thermochemistry,...
-
electricityElectricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge...
, abbreviated as
TE) refers to a class of phenomena in which a
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
difference creates an
electric potentialAt a point in space, the electric potential is potential energy divided by charge that is associated with a static electric field. It is a scalar quantity, typically measured in volts....
or an electric potential creates a temperature difference. In modern technical usage, the term almost always refers collectively to the Seebeck effect, Peltier effect, and the Thomson effect.
- This page is about devices that use the thermoelectric effect. For the physics underlying the thermoelectric effect, see thermoelectric effect
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely when a voltage is applied to it, it creates a temperature difference...
.
Thermoelectricity (
thermoThermo, descended from , meaning heat, is a prefix referring to heat or temperature, e.g.,* thermodynamics, the physics of energy, heat, work, and entropy, which is also discussed in the article heat* thermochemistry,...
-
electricityElectricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge...
, abbreviated as
TE) refers to a class of phenomena in which a
temperatureIn physics, temperature is a physical property of a system that underlies the common notions of hot and cold; something that feels hotter generally has the higher temperature. Temperature is one of the principal parameters of thermodynamics...
difference creates an
electric potentialAt a point in space, the electric potential is potential energy divided by charge that is associated with a static electric field. It is a scalar quantity, typically measured in volts....
or an electric potential creates a temperature difference. In modern technical usage, the term almost always refers collectively to the Seebeck effect, Peltier effect, and the Thomson effect. Analyzing the word
thermoelectricity by its etymological components, it might be taken to refer generically to all heat engines that are used to generate
electricityElectricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge...
and all electrically powered heating devices, for which there is an almost arbitrary number of conceivable techniques, but in practice such a broad use of the term is seldom encountered.
In recent years, thermoelectricity sees rapidly increasing usages in applications like portable refrigerators, beverage coolers, electronic component coolers, metal alloy sorting devices etc. One of the most commonly used material in such application is
Bismuth tellurideBismuth telluride is a gray powder that is a compound of bismuth and tellurium also known as bismuth telluride. It is a semiconductor which is an efficient thermoelectric material for refrigeration or portable power generation.-Thermoelectric properties:Bismuth telluride is a narrow gap layered...
(Bi
2Te
3), a chemical compound of
bismuthBismuth is a chemical element that has the symbol Bi and atomic number 83. This trivalent poor metal chemically resembles arsenic and antimony. Bismuth is heavy and brittle; it has a silvery white color with a pink tinge owing to the surface oxide. Bismuth is the most naturally diamagnetic of all...
and
telluriumTellurium is a chemical element that has the symbol Te and atomic number 52. A brittle silver-white metalloid which looks similar to tin, tellurium is chemically related to selenium and sulfur. Tellurium is primarily used in alloys and as a semiconductor.-Characteristics:Tellurium is extremely...
.
Motivation for research
Currently there are two primary arenas in which thermoelectric devices can lend themselves to increase energy efficiency and/or decrease pollutants: conversion of waste heat into usable energy and refrigeration.
Power generation
In the transportation sector, although very common as a means of powering vehicles, internal combustion engines are highly inefficient in energy use (using only 20-25% of the energy generated during fuel combustion). Furthermore, the electricity requirement in vehicles is increasing due to the demands of enhanced performance, on-board controls and creature comforts (stability controls, telematics, navigation systems, electronic braking, etc.). In order to gain fuel efficiency, it may be possible to shift energy draw from the engine (in certain cases) to the electrical load in the car, e.g. electrical power steering or electrical coolant pump operation. Thermoelectric devices are thus being investigated to convert waste-heat into usable energy using the Seebeck Effect.
Currently, some power plants use a method known as
cogenerationCogeneration is the use of a heat engine or a power station to simultaneously generate both electricity and useful heat...
in which in addition to the electrical energy generated, the heat produced during the process is used for alternative purposes. Thermoelectrics may find applications in such systems or in
solar thermal energySolar thermal energy is a technology for harnessing solar energy for thermal energy . Solar thermal collectors are defined by the USA Energy Information Administration as low-, medium-, or high-temperature collectors. Low temperature collectors are flat plates generally used to heat swimming pools...
generation.
Refrigeration
Thermoelectric devices applied to refrigeration using the Peltier effect could reduce the emission of ozone-depleting refrigerants into the atmosphere. Hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs) are known ozone depleting substances (ODSs); however, these chemicals have long been at the heart of refrigeration technology. Recently, there has been legislation regulating the use of such chemicals for refrigeration; current international legislation mandates caps on HCFC production and will prohibit their production after 2020 in developed countries and 2030 in developing countries. These mandates as well as the environmental mindedness of consumers is leading to an increased effort in developing effective thermoelectric refrigeration units. Such units could reduce the use of such harmful chemicals and would operate more quietly (since they are solid state and do not require noisy compressors.) Vapor compression refrigerators are still more efficient than peltier refrigerators, but they are larger, and require more maintenance.
Figure of merit
The primary criterion for thermoelectric device viability is the
figure of meritA figure of merit is a quantity used to characterize the performance of a device, system or method, relative to its alternatives. In engineering, figures of merit are often defined for particular materials or devices in order to determine their relative utility for an application...
given by:,
which depends on the
Seebeck coefficientSeebeck is the family name of several people:* August Seebeck scientist* Nicholas F. Seebeck stamp printer* Thomas Johann Seebeck physicistThe Seebeck Effect is a form of thermoelectric effect...
, ,
thermal conductivityIn physics, thermal conductivity, , is the property of a material that indicates its ability to conduct heat. It appears primarily in Fourier's Law for heat conduction.-Measurement:...
, , and
electrical conductivityElectrical conductivity or specific conductance is a measure of a material's ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current...
, .
Slack's proposal: Phonon-Glass, electron-crystal (PGEC) behavior
Notably, in the above equation,
thermal conductivityIn physics, thermal conductivity, , is the property of a material that indicates its ability to conduct heat. It appears primarily in Fourier's Law for heat conduction.-Measurement:...
and
electrical conductivityElectrical conductivity or specific conductance is a measure of a material's ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current...
are typically intertwined. G. A. Slack proposed that in order to optimize the figure of merit, phonons which are responsible for thermal conductivity must experience the material as they would in a glass (experiencing a high degree of
phononIn physics, a phonon is a quantized mode of vibration occurring in a rigid crystal lattice, such as the atomic lattice of a solid. The study of phonons is an important part of solid state physics, because phonons play a major role in many of the physical properties of solids, including a material's...
scattering--lowering the
thermal conductivityIn physics, thermal conductivity, , is the property of a material that indicates its ability to conduct heat. It appears primarily in Fourier's Law for heat conduction.-Measurement:...
) while electrons must experience it as a
crystalA crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography...
(experiencing very little scattering--maintaining the
electrical conductivityElectrical conductivity or specific conductance is a measure of a material's ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current...
). It is through the adjustment of each these properties independently of the other that the figure of merit can be improved.
Materials of interest
There are a number of materials being researched for thermoelectric device applications and temperature ranges. Some such materials include:
Bismuth chalcogenides
These materials involve
Bi2Te3Bismuth telluride is a gray powder that is a compound of bismuth and tellurium also known as bismuth telluride. It is a semiconductor which is an efficient thermoelectric material for refrigeration or portable power generation.-Thermoelectric properties:Bismuth telluride is a narrow gap layered...
and Bi
2Se
3 and comprise some of the best performing thermoelectrics at room temperature with a temperature-independent
figure of meritThe thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely when a voltage is applied to it, it creates a temperature difference...
, ZT, between 0.8 and 1.0. Nanostructuring of these materials to produce a layered superlattice structure of alternating
Bi2Te3Bismuth telluride is a gray powder that is a compound of bismuth and tellurium also known as bismuth telluride. It is a semiconductor which is an efficient thermoelectric material for refrigeration or portable power generation.-Thermoelectric properties:Bismuth telluride is a narrow gap layered...
and Bi
2Se
3 layers produces a device within which there is good electrical conductivity but perpendicular to which thermal conductivity is poor. The result is an enhanced ZT (approximately 2.4 at room temperature for p-type). Note that this high value has not entirely been independently confirmed.
Skutterudite thermoelectrics
Recently,
skutteruditeSkutterudite is a naturally occurring cobalt arsenide mineral. The crystal structure of this mineral has been found to have important technological uses for several compounds isostructural with the mineral.-The skutterudite mineral:...
materials have sparked the interest of researchers in search of new thermoelectrics These structures are of the form (Co,Ni,Fe)(P,Sb,As)
3 and are cubic with
space groupIn crystallography, the space group of a crystal is a description of the symmetry of the crystal, and can have one of 230 types...
Im3. Unfilled, these materials contain voids into which low-coordination ions (usually rare earth elements) can be inserted in order to alter thermal conductivity by producing sources for lattice phonon scattering and decrease thermal conductivity due to the lattice without reducing electrical conductivity. Such qualities make these materials behave with PGEC behavior.
Oxide thermoelectrics
Due to the natural superlattice formed by the layered structure in homologous compounds (such as those of the form (SrTiO3)
n(SrO)
m--the Ruddleson-Popper phase), oxides are also being considered for high-temperature thermoelectric devices. These materials exhibit low thermal conductivity perpendicular to these layers while maintaining electrical conductivity within the layers. The figure of merit in oxides is yet relatively low (~0.34 at 1000K), but the enhanced thermal stability, as compared to conventional high-ZT bithmuth compounds, makes the oxides superior in high-temperature applications.
Nanomaterials
In addition to the nanostructured Bi
2Te
3/Bi
2Se
3 superlattice thin films that have shown a great deal of promise, other nanomaterials have also shown potential in improving thermoelectric materials. One example involving PbTe/PbSeTe quantum dot superlattices was shown to provide an enhanced ZT (approximately 1.5 at room temperature) that was a great deal higher than the bulk ZT value for either PbTe or PbSeTe (approximately 0.5). More recently, two research groups have shown that individual silicon nanowires can act as efficient thermoelectric materials. Each group found ZT values approaching 1.0 for their structures, even though bulk silicon is known to be a poor thermoelectric material (approximately 0.01 at room temperature) because of its high thermal conductivity.
See also
- Thermoelectric effect
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely when a voltage is applied to it, it creates a temperature difference...
- Thermopower
The thermopower, or thermoelectric power of a material is a measure of the magnitude of an induced thermoelectric voltage in response to a temperature difference across that material...
- Batteryless radio
Radio receivers were originally operated by battery. The term batteryless radio was initially used for the radio receivers which could be used directly by AC mains supply ....
- Joule's law
Joule's laws are a pair of laws concerning the heat produced by a current and the energy dependence of an ideal gas to that of pressure, volume, and temperature, respectively....
- Heat transfer
Heat transfer is the transition of thermal energy from a hotter object to a cooler object...
- Thermoelectric cooling
Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other side against the...
/ Peltier device
- Pyroelectric effect
- Thermogenerator
Thermogenerators are devices which convert heat directly into electrical energy. For the most part, this term is synonymous with "thermoelectric generator" and rarely used in English. Essentially they work on the principle of the Seebeck effect, with typical efficiencies of around 5-10%...
- Thermionic emission
Thermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the forces restraining it. The charge carriers can be electrons or ions, and in older literature are sometimes...
- Bismuth telluride
Bismuth telluride is a gray powder that is a compound of bismuth and tellurium also known as bismuth telluride. It is a semiconductor which is an efficient thermoelectric material for refrigeration or portable power generation.-Thermoelectric properties:Bismuth telluride is a narrow gap layered...
External links