Organic Molecules in a Box—Barocaloric Cooling from Confined Order-Disorder Transitions

As the societal impact on the environment grows, we urgently need solutions to address climate change. In particular, we must develop eco-friendly approaches to thermal management from indoor environments to food and medicine storage and instrument operation. Barocaloric materials, wherein the solid-solid phase transitions may be controlled with pressure, offer a sustainable, emissions-free heating and cooling platform that could interface with existing vapor-compression cooling infrastructure. However, the phase transitions of barocaloric materials generally exhibit low sensitivity to pressure and significant phase transition hysteresis, which necessitate the use of prohibitively large pressures (>>100 bar) to reversibly induce heating or cooling cycles. Previous work has demonstrated the efficacy of using three-dimensionally confined order-disorder transitions of organic cations to modify phase transition pressure sensitivities. In this work, we aim to elucidate the underlying structure-property relationships that control pressure sensitivity in related three-dimensional perovskite-like materials, wherein inorganic cages act to confine organic cations that undergo order-disorder transitions. Such variations modify both the free volume of the cage and non-covalent interaction strength between confined cations and their surrounding cages. As a result, the order-disorder transitions range from 200–400 K and, with proper selection of the confined cation, yield entropy changes of >100 J kg⁻¹ K⁻¹ and ultralow thermal hysteresis. Further, we will demonstrate how pressure sensitivity and thermal transport may be modulated based on metal node and central cations compositions in these material architectures. The cumulative results allow us to modify this thermally and chemically stable class of materials for optimal barocaloric design.