Reversible low-pressure barocaloric effect from mixed-phase stabilization in a hybrid cadmium perovskite

Pressure-driven phase transitions provide a means to modulate entropy in solids, although achieving large and reversible caloric responses remains a central challenge. The layered hybrid organic-inorganic perovskite (C 9 H 19 NH 3 ) 2 CdCl 4 exhibits two first-order transitions near room temperature that underpin its barocaloric response. High-pressure calorimetry combined with synchrotron X-ray diffraction shows that compression stabilizes a mixed-phase region over a wide pressure-temperature range rather than inducing a complete transformation. Consequently, the effective entropy change decreases with pressure, while a substantial reversible contribution is preserved, yielding reversible entropy and temperature changes of Δ Sᵣ e ᵥ ≈ 136 J kg −1 K −1 and Δ Tᵣ e ᵥ ≈ 17 K for a pressure change of 0.8 kbar. This leads to a refrigerant capacity exceeding 4 kJ kg −1 with a favorable coefficient of performance in the low-pressure regime. Notably, the large reversible temperature changes achieved at moderate pressures and close to room temperature highlight the potential of this material for solid-state cooling. Overall, these results demonstrate that high caloric performance can be achieved without complete phase transformation, reflecting a trade-off between entropy change and reversibility enabled by the structural flexibility of hybrid organic-inorganic materials.