Physics:Electrocaloric effect
The electrocaloric effect is a 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. It should not be confused with the Thermoelectric effect (specifically, the Peltier effect), in which a temperature difference occurs when a current is driven through an electric junction with two dissimilar conductors.
The underlying mechanism of the effect is not fully established; in particular, different textbooks give conflicting explanations.[1] However, as with any isolated (adiabatic) temperature change, the effect comes from the voltage raising or lowering the entropy of the system.[2] (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 volts.[1]
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 as much as ~12 K (12 °C) for an electric field change of 480 kV/cm, at an ambient temperature of 220 °C (430 °F).[1] The device structure consisted of a thin film (PZT) on top of a much thicker substrate, but the figure of 12 K represents the cooling of the thin film only. The net cooling of such a device would be lower than 12 K 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 also achieve 12 K of cooling, nearer to room temperature (yet above 70 °C) than PZT.[3]
With these new, larger responses, practical applications may be more likely, such as in computer cooling or batteries.[4] In the long-term the electrocaloric effect might moreover be used in high-efficiency heat pumps.[5]
References
- ↑ 1.0 1.1 1.2 A. S. Mischenko (March 2006). "Giant Electrocaloric Effect in Thin-Film PbZr0.95Ti0.05O3". Science 311 (5765): 1270–1271. doi:10.1126/science.1123811. PMID 16513978. Bibcode: 2006Sci...311.1270M. http://www.sciencemag.org/cgi/content/full/311/5765/1270.
- ↑ See Reif
- ↑ Neese, B.; Chu, B.; Lu, S. -G.; Wang, Y.; Furman, E.; Zhang, Q. M. (2008). "Large Electrocaloric Effect in Ferroelectric Polymers Near Room Temperature". Science 321 (5890): 821–823. doi:10.1126/science.1159655. PMID 18687960. Bibcode: 2008Sci...321..821N., alternate web link.
- ↑ Fairley, Peter (14 September 2017). "A Solid-State Fridge in Your Pocket". IEEE Spectrum. https://spectrum.ieee.org/energywise/consumer-electronics/portable-devices/a-solid-state-fridge-in-your-pocket.
- ↑ "ElKaWe – Electrocaloric heat pumps" (in en). https://www.fraunhofer.de/en/research/lighthouse-projects-fraunhofer-initiatives/fraunhofer-lighthouse-projects/elkawe.html.
Further reading
- Scott, J. F. (2011). "Electrocaloric Materials". Annual Review of Materials Research 41: 229–240. doi:10.1146/annurev-matsci-062910-100341. Bibcode: 2011AnRMS..41..229S.
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