Exploring the elastocaloric switching effect and its mechanism

Refrigeration currently relies on vapor compression technology, but researchers are investigating solid-state refrigeration technology as a more efficient and eco-friendly alternative.

The elastocaloric effect, a phenomenon in which a material releases or absorbs heat when stress is applied, holds promise in advancing solid-state refrigeration technology. Odaira et al. found that Co-Cr-Al-Si alloys demonstrate a unique property related to the elastocaloric effect, known as elastocaloric switching.

In the conventional elastocaloric effect, materials release heat when stress is applied. But some materials demonstrate the opposite effect, cooling down when stress is applied. The Co-Cr-Al-Si alloys exhibit both: at room temperature, the material displays the conventional effect and heats under stress; at lower temperatures, such as from 100-200 K, the material would cool under stress. The sign of the elastocaloric effect changes depending on the temperature.

The authors identified reentrant martensitic transformation as the underlying mechanism of the elastocaloric switching effect. In conventional martensitic transformation, a one-way parent-to-martensite transition occurs during cooling. In reentrant martensitic transformation, a successive parent-to-martensite-to-parent transition occurs during cooling, consistent with their observation of the flip-flopping effect in the alloy.

“Our findings in this work can provide new possibilities for the design of the elastocaloric systems in future technologies,” said author Xiao Xu. The elastocaloric effect of the Co-Cr-Al-Si alloys is too small for practical use, so next the authors will look for materials with higher refrigeration capabilities, as well as increased durability.

Source: “Elastocaloric switching effect induced by reentrant martensitic transformation,” by Takumi Odaira, Sheng Xu, Xiao Xu, Toshihiro Omori, and Ryosuke Kainuma, Applied Physics Reviews (2020). The article can be accessed at https://doi.org/10.1063/5.0007753 .