Double barocaloric effects in ferroelastic Pb3V2O8

Barocaloric (BC) materials are a category of solid-state refrigerants with great potential for use in future refrigerators. Here we reported the double BC effects in ferroelastic Pb₃V₂O₈. Upon heating, it undergoes a transition from the distorted monoclinic α phase to monoclinic β phase at 273 K, and then the β phase transfers to the rhombhedral γ phase at 375 K. Applying pressure shifts the α-β and β-γ transitions to higher and lower temperatures, respectively. By applying a pressure of 100 MPa, the isothermal entropy changes are -6.4 JK^-1kg^-1 and 11.6 JK^-1kg^-1 for the α-β and β-γ transitions, corresponding to the adiabatic temperature change of 5.9 K and -9.7 K, respectively. The conventional and inverse BC effects are attributed to the lattice expansion and contraction during the α-β and β-γ transitions, respectively. Such double BC effects enable automatic switching between cooling and heating modes according to the changes of ambient temperature.