Colossal Reversible Barocaloric Effects in a Plastic Crystal Mediated by Lattice Vibrations and Ion Diffusion

M Zeng and C Escorihuela-Sayalero and T Ikeshoji and S Takagi and S Kim and SI Orimo and M Barrio and JL Tamarit and P Lloveras and C Cazorla and K Sau, ADVANCED SCIENCE, 11 (2024).

DOI: 10.1002/advs.202306488

Solid-state methods for cooling and heating promise a sustainable alternative to current compression cycles of greenhouse gases and inefficient fuel-burning heaters. Barocaloric effects (BCE) driven by hydrostatic pressure (p) are especially encouraging in terms of large adiabatic temperature changes (|Delta T| approximate to 10 K) and isothermal entropy changes (|Delta S| approximate to 100 J K-1 kg-1). However, BCE typically require large pressure shifts due to irreversibility issues, and sizeable |Delta T| and |Delta S| seldom are realized in a same material. Here, the existence of colossal and reversible BCE in LiCB11H12 is demonstrated near its order-disorder phase transition at approximate to 380 K. Specifically, for Delta p approximate to 0.23 (0.10) GPa, |Delta Srev| = 280 (200) J K-1 kg-1 and |Delta Trev| = 32 (10) K are measured, which individually rival with state-of-the-art BCE figures. Furthermore, pressure shifts of the order of 0.1 GPa yield huge reversible barocaloric strengths of approximate to 2 J K-1 kg-1 MPa-1. Molecular dynamics simulations are performed to quantify the role of lattice vibrations, molecular reorientations, and ion diffusion on the disclosed BCE. Interestingly, lattice vibrations are found to contribute the most to |Delta S| while the diffusion of lithium ions, despite adding up only slightly to the entropy change, is crucial in enabling the molecular order-disorder phase transition. The presence of colossal and reversible barocaloric effects in LiCB11H12, a renowned solid electrolyte, is evidenced near its order-disorder phase transition. It is observed that lattice vibrations primarily contribute to these barocaloric effects. Additionally, although the diffusion of lithium ions only marginally contributes to the accompanying entropy change, it plays a crucial role in facilitating the molecular order- disorder phase transition. image

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