Ultrasensitive barocaloric material for room-temperature solid-state refrigeration

One of the greatest obstacles to the real application of solid-state refrigeration is the huge driving fields. Here, we report a giant barocaloric effect in inorganic NH 4 I with reversible entropy changes of \(\Delta {S}_{{P}_{0}\to P}^{{{\max }}}\) ∼ 71 J K −1 kg −1 around room temperature, associated with a structural phase transition. The phase transition temperature, T t , varies dramatically with pressure at a rate of d T t /d P ∼ 0.79 K MPa −1 , which leads to a very small saturation driving pressure of Δ P ∼ 40 MPa, an extremely large barocaloric strength of \(\left|\Delta {S}_{{P}_{0}\to P}^{{{\max }}}/\Delta P\right|\) ∼ 1.78 J K −1 kg −1 MPa −1 , as well as a broad temperature span of ∼ 41 K under 80 MPa. Comprehensive characterizations of the crystal structures and atomic dynamics by neutron scattering reveal that a strong reorientation-vibration coupling is responsible for the large pressure sensitivity of T t . This work is expected to advance the practical application of barocaloric refrigeration.