Semiconductor cooling is a promising alternative cooling technique that does not rely on the use of gases or liquids, like conventional refrigeration systems, but instead uses the properties of solid materials to refrigerate. This alternative cooling approach could be very energy efficient and help refrigerate objects without releasing greenhouse gases into the air.
Despite their potential, conventional caloric effects have proven difficult to implement effectively in real-world refrigeration devices. This is because they are only significant in a narrow temperature range and have specific requirements that limit the possibilities of the resulting cooling systems.
Researchers from the Institut de Ciència de Materials de Barcelona and the Universitat Politècnica de Catalunya recently proposed a possible solution to overcome the limitations of existing solid-state cooling systems. Their article, published in Physical Examination Letterstheoretically demonstrates that certain ferroelectric perovskites could exhibit giant photocaloric (PC) effects, which persist over a much wider temperature range than conventional caloric effects.
“Our inspiration came from two different sources,” Claudio Cazorla, co-author of the paper, told Phys.org. “On the one hand, we were aware of the possibility of inducing phase transitions in ferroelectrics by highlighting them and had already explored this idea by proposing new thermal switch mechanisms. On the other hand, we interests in semiconductor cooling and heat-intensive materials, promising to replace current refrigeration technologies based on environmentally harmful gas compression/decompression cycles.
Caloric materials typically used to achieve solid-state cooling undergo phase transitions under external fields. These transitions change the entropy of these materials and can be exploited to induce refrigeration and heat pumping.
Building on their interest in ferroelectric and caloric materials, Cazorla and his colleagues set out to explore the possible existence of PC effects in ferroelectric materials, which would essentially enable the cooling of solids by light irradiation. The main objective of their recent study was to theoretically characterize these PC effects and determine whether they could be of practical interest for the development of refrigeration systems.
“Although the idea of inducing phase transitions in ferroelectrics with light has been around for a while, I came across it by chance during a workshop in 2021,” said Riccardo Rurali, co-author of the article, at Phys.org.
“This immediately caught my attention, because I thought it could be used to design a thermal switch (my main “research activity”), where, through the absorption of light, one could shuttle between a high thermal conductivity state and a low state Fortunately, Claudio Cazorla realized that the same phase transition induced by light was accompanied by a huge change in entropy and therefore could be used to design. an extremely efficient PC cycle, which greatly outperforms the thermal switch we previously proposed.
PC effects could have various advantages over other caloric effects, such as magnetocaloric, electrocaloric, and mechanocaloric effects. Most notable is that PC effects are large and can be exploited over a much wider temperature range.
In fact, the effects described in the team’s paper have been theoretically shown to remain significant over wide temperature intervals, on the order of 100K. On the other hand, conventional caloric effects are only active over narrow temperature intervals of the order of 10K.
“The condition for the light-induced PC effect to work is that the system transitions from a ferroelectric state to a paraelectric state, that is, it loses its spontaneous electrical polarization upon absorption of light,” Cazorla explained. “Therefore, the temperature range in which the effects of PC can be observed corresponds to the temperature range in which the material is ferroelectric, which can reach several hundred degrees Kelvin.”
In their paper, Cazorla, Rurali and their colleagues predict the existence of PC effects in certain ferroelectric materials. Notably, these effects are assumed to occur in only a few polar materials, including the archetypal ferroelectric BaTiO.3 and KNbO3.
“The fact that the triggering field for PC effects is light absorption implies that there is no need to deposit electrodes on the surfaces of the ferroelectric material,” Cazorla said. “This could greatly simplify the design and manufacturing of the corresponding practical setup. Additionally, PC effects are very well suited to miniaturization since the necessary light source can be obtained with lasers.”
The PC effects theoretically demonstrated in this recent paper may soon be examined in more detail and investigated experimentally. Cazorla, Rurali and their colleagues suggest that these effects would be particularly suited to microscale cooling applications, such as the refrigeration of central processing units (CPUs) and other circuit components.
Furthermore, as these effects are assumed to persist over broad temperature intervals, from room temperature to absolute zero, they could also be exploited to achieve cryogenic cooling (i.e., down to ultra-high temperatures). bass). Cryogenic cooling could in turn prove very useful for the realization of quantum technologies.
“Currently, we are exploring families of materials other than ferroelectrics that can also exhibit light-induced phase transitions with potential for solid-state cooling applications,” Cazorla said. “In addition, we consider the role of dimensionality in bringing PC effects into real-world applications (e.g., two-dimensional materials and thin films).”
Cazorla, Rurali, and their colleagues are currently conducting additional studies aimed at further evaluating the potential of the PC effects they theorized, while also considering potential strategies for exploiting them in real-world applications. Their study could inspire other teams to also explore these effects and their potential for improving semiconductor cooling.
“We realized that photoinduced charging can suppress other ordered charge states that couple to the network structure,” Rurali added. “Currently, we are studying 2D materials featuring charge density waves (CDW). They are particularly promising because, due to their dimensionality, they seem better suited to efficiently absorb light.”
More information:
Riccardo Rurali et al, Giant photocaloric effects over a wide temperature range in ferroelectric perovskites, Physical Examination Letters (2024). DOI: 10.1103/PhysRevLett.133.116401. On arXiv: DOI: 10.48550/arxiv.2404.05562
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