Electrocaloric cooling is a high-efficiency, carbon-free alternative for refrigeration with zero global warming potential. The cooling power is achieved by engineering phase transition in materials. However, a better understanding of the phenomenon is required for widespread implementation.

Liu et al. employ a fully first-principles method to understand this phenomenon and disclose that the negative electrocaloric effect originates from the latent heat associated with phonon entropy. Using this new finding to engineer entropy modifications can significantly enhance the cooling power density.

Until now, dipolar entropy has been widely used to explain the cooling effect. Because dipolar entropy is difficult to calculate directly, it can only operate as a qualitative rule. In this work, the authors derive phonon frequency cumulative phonon entropy, which can serve as a quantitative rule to optimize the technology.

“During the antiferroelectric-ferroelectric (AFE-FE) phase transition, the lattice structure has a large change,” said author Chenhan Liu. “As a result, phonon entropy increases, which results in the negative electrocaloric effect. This simple relation was ignored in previous studies.”

The team extracts the phonon entropy evolution along the AFE-FE phase transition path by simulating the transition on PbZrO3, a commonly used antiferroelectric material. After determining the origin of the negative electrocaloric effect, they proposed a new concept of phonon entropy engineering that can notably increase cooling efficiency.

“I will explore phonon entropy and electrocaloric cooling in other antiferroelectric materials and employ this principle in experiment.” Said Liu. “More importantly, I want to extend the concept of phonon entropy to other physical phenomena.”

Source: “Phonon entropy engineering for caloric cooling,” by Chenhan Liu, Yangyang Si, Menglong Hao, Yi Tao, Shiqing Deng, Ping Lu, Chuanwen Zhao, Zuhuang Chen, Gang Zhang, and Yunfei Chen, Applied Physics Reviews (2023). The article can be accessed at https://doi.org/10.1063/5.0152301.