International. Phase transitions take place with the exchange of heat (i.e., entropy) between materials and environments. When such processes are pressure-driven, the induced cooling effect is called the barocaloric effect, which is a promising alternative to the conventional vapor compression cycle.
For the purpose of actual application, it is desirable for a material to have major entropy changes induced by lower pressure.
Recently, an international research team led by Prof. LI Bing of the Metal Research Institute of the Chinese Academy of Sciences found that a class of disordered materials, called plastic crystals, exhibit large barocaloric effects under very weak pressure.
Typical entropy changes are several hundred joules per kilogram per kelvin, which is ten times better than previous materials.
Using large-scale facilities in Japan and Australia, the team revealed that the constituent molecules of these materials are very disoriented in the networks and are inherently easy to deform.
As a result, a small pressure can suppress the extensive orientation disorder and thus pressure-induced entropy changes are obtained. These two merits make plastic crystals the best barocaloric materials so far.
This research presents the first report that entropy changes can exceed 100 joules per kilogram per kelvin and represent the best among all caloric effect materials (barocaloric effect and its analogies such as the magnetocaloric effect, the electrocaloric effect and the elastocaloric effect), considered as a milestone.
The microscopic physical scenario established using the neutron scattering technique is useful for designing even better materials in the future.
As far as the refrigeration application is concerned, the plastic crystals reported here are very promising given that they are abundantly available, environmentally friendly, easy to handle and high performance.
This work points in a new direction for emerging solid-state cooling technologies.
Source: Chinese Academy of Sciences.
