New material cools under pressure

The barocaloric effect refers to the change in temperature produced in a material by the application of hydrostatic pressure. Most objects heat up when compressed and cool down when decompressed, but some solids display the opposite behaviour: their temperature decreases when they are compressed and increases when they are decompressed. Lluís Mañosa, UB professor, explains: "This highly unusual behaviour is what we have termed the inverse barocaloric effect. In our study we have found a material which exhibits a substantial change at moderate pressures: its temperature drops by 1ºC for each additional 1 kbar of pressure."

During the study, the Group on Characterization of Materials at the Polytechnic University of Catalonia. BarcelonaTech (UPC) carried out a characterization of the processes to which the solid material was submitted, at different temperatures and pressures, using a custom system developed by the team.

The material developed during the study is an intermetallic compound of the magnetocaloric metals lanthanum, iron, silicon and cobalt (La-Fe-Si-Co), which change temperature when an external magnetic field is applied. This group of materials is considered to be the most promising for novel refrigeration systems. According to Mañosa, "in the material we studied, the temperature change brought about by moderate pressures is of sufficient magnitude to be considered for use in environmentally respectful refrigeration systems. In addition, the fact that it responds to two types of external stimulus -- magnetic fields and pressure -- would allow for the design of devices that apply these stimuli simultaneously to obtain higher levels of performance."

The inverse barocaloric effect is created by a phase transition in the material below a given temperature, which leads to changes in its structural and magnetic properties. It has recently been suggested that materials displaying this behaviour could also be used in novel energy harvesting systems.