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

Area of Science:

• Materials Science
• Thermodynamics
• Solid-state Physics

Background:

• Solid-state cooling/heating offers a sustainable alternative to current technologies.
• Barocaloric effects (BCE) driven by hydrostatic pressure (p) show promise for large temperature and entropy changes.
• Challenges include large pressure shifts and realizing significant |ΔT| and |ΔS| in the same material.

Purpose of the Study:

• To demonstrate colossal and reversible BCE in LiCB11H12.
• To investigate BCE near the material's order-disorder phase transition at ~380 K.
• To quantify the contributions of lattice vibrations, molecular reorientations, and ion diffusion to BCE.

Main Methods:

• Experimental measurement of adiabatic temperature changes (|ΔT|) and isothermal entropy changes (|ΔS|) under hydrostatic pressure.
• Utilizing molecular dynamics simulations to analyze the underlying mechanisms of BCE.
• Investigating the role of lattice vibrations, molecular reorientations, and ion diffusion.

Main Results:

• Colossal and reversible BCE demonstrated in LiCB11H12 near 380 K.
• Achieved |ΔS_rev| = 280 J K⁻¹ kg⁻¹ and |ΔT_rev| = 32 K for Δp ≈ 0.23 GPa.
• High reversible barocaloric strength of ≈2 J K⁻¹ kg⁻¹ MPa⁻¹ observed for Δp ≈ 0.1 GPa.
• Lattice vibrations significantly contribute to |ΔS|, while lithium ion diffusion is crucial for the phase transition.

Conclusions:

• LiCB11H12 exhibits state-of-the-art colossal barocaloric effects, rivaling current benchmarks.
• The material offers a promising avenue for efficient and sustainable solid-state cooling and heating applications.
• Understanding the interplay of lattice dynamics and ion diffusion is key to optimizing BCE materials.