Colossal Barocaloric Effects at Triple-Phase Points

Abstract

Barocaloric effect underlies a promising emission-free and highly efficient cooling technology. The current wisdom to design barocaloric materials is to find materials undergoing a temperature-induced phase transition with huge latent heats and then to apply a pressure to harvest the heat. So far, the entropy change of the temperature-induced phase transition usually sets the upper limit for the barocaloric effect. Here we proposed and realized a large barocaloric effect at approaching a triple-phase point in odd-numbered n-alkanes. A low pressure can drive the phase transition from the liquid state to the disordered solid state and the phase transition from the disordered solid state to the ordered solid state to be merged at 297 K. These phase transition behaviors are well explained by in-situ Raman scattering and complementary molecular dynamics simulations. Around such a point, an adiabatic temperature change as large as ~30 K has been achieved under 150 MPa. The high coefficient of phase transition temperature with respect to pressure makes the triple-phase-point temperature to be continuously tuned by pressure and a wide refrigeration temperature window of more than 50 K (280–335 K) was realized. The strategy could initiate a new research avenue and shed light on designing novel high-performance barocaloric materials.