Electrocaloric effect
Encyclopedia
The electrocaloric effect is phenomenon in which a material shows a reversible temperature change under an applied electric field. It is often considered to be the physical inverse of the pyroelectric effect.
The underlying mechanism of the effect is not fully established; in particular, different textbooks give conflicting explanations. However, as with any isolated (adiabatic) temperature change, the effect comes from the voltage raising or lowering the entropy
of the system. (The magnetocaloric effect is an analogous, but better-known and understood, phenomenon.)
Electrocaloric materials were the focus of significant scientific interest in the 1960s and 1970s, but were not commercially exploited as the electrocaloric effects were insufficient for practical applications, the highest response being 2.5 degrees Celsius under an applied potential of 750 volt
s.
In March 2006 it was reported in the journal Science
that thin films of the material PZT (a mixture of lead
, titanium
, oxygen
and zirconium
) showed the strongest electrocalorific response yet reported, with the materials cooling down by up to 12 °F (7 °C) in a field of just 25 volts, at an ambient temperature of 220 °C (430 °F). The device structure consisted of a thin film (PZT) on top of a much thicker substrate, but the figure of 7°C represents the cooling of the thin film only. The net cooling of such a device would be lower than 7°C due to the heat capacity of the substrate to which it is attached.
Along the same lines, in 2008, it was shown that a ferroelectric polymer can achieve 12 °C of cooling, near room temperature.
With these new, larger responses, practical applications may be more likely, such as in computer cooling
.
The underlying mechanism of the effect is not fully established; in particular, different textbooks give conflicting explanations. However, as with any isolated (adiabatic) temperature change, the effect comes from the voltage raising or lowering the entropy
Entropy
Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...
of the system. (The magnetocaloric effect is an analogous, but better-known and understood, phenomenon.)
Electrocaloric materials were the focus of significant scientific interest in the 1960s and 1970s, but were not commercially exploited as the electrocaloric effects were insufficient for practical applications, the highest response being 2.5 degrees Celsius under an applied potential of 750 volt
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
s.
In March 2006 it was reported in the journal Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....
that thin films of the material PZT (a mixture of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...
) showed the strongest electrocalorific response yet reported, with the materials cooling down by up to 12 °F (7 °C) in a field of just 25 volts, at an ambient temperature of 220 °C (430 °F). The device structure consisted of a thin film (PZT) on top of a much thicker substrate, but the figure of 7°C represents the cooling of the thin film only. The net cooling of such a device would be lower than 7°C due to the heat capacity of the substrate to which it is attached.
Along the same lines, in 2008, it was shown that a ferroelectric polymer can achieve 12 °C of cooling, near room temperature.
With these new, larger responses, practical applications may be more likely, such as in computer cooling
Computer cooling
Computer cooling is required to remove the waste heat produced by computer components, to keep components within their safe operating temperature limits.Various cooling methods help to improve processor performance or reduce the noise of cooling fans....
.