Colossal barocaloric effects in the complex hydride Li${}_2$B${}_{12}$H${}_{12}$

Abstract

Traditional refrigeration technologies based on compression cycles of greenhouse gases pose serious threats to the environment and cannot be downscaled to electronic device dimensions. Solid-state cooling exploits the thermal response of caloric materials to external fields and represents a promising alternative to current refrigeration methods. However, most of the caloric materials known to date present relatively small adiabatic temperature changes ($|\Delta T|\sim 1$ K) and/or limiting irreversibility issues resulting from significant phase-transition hysteresis. Here, we predict the existence of colossal barocaloric effects (isothermal entropy changes of $|\Delta S|\sim 100$ JK${}^{-1}$kg${}^{-1}$) in the energy material Li${}_2$B${}_{12}$H${}_{12}$ by means of molecular dynamics simulations. Specifically, we estimate $|\Delta S|=387$ JK${}^{-1}$kg${}^{-1}$ and $|\Delta T|=26$ K for an applied pressure of $P=0.4$ GPa at $T=475$ K. The disclosed colossal barocaloric effects are originated by an order-disorder phase transformation that exhibits a fair degree of reversibility and involves coexisting Li${}^{+}$ diffusion and (BH)${}_{12}^{-2}$ reorientational motion at high temperatures.

8 pages, 3 figures, 1 table