Reversible colossal barocaloric effect in methylphosphonium tin bromide for room-temperature refrigeration

X Xu and C Niu and GW Zhai and M Li and XH Lin and H Wang, PHYSICAL REVIEW B, 111, 224113 (2025).

DOI: 10.1103/47b3-yzfm

Solid-state refrigeration promises for environmentally friendly cooling with high energy efficiency and compact design scalability. However, its refrigeration performance (e.g., isothermal entropy change and adiabatic temperature change) is inferior particularly near room temperature (RT), which greatly hinders the practical application. Utilizing first- principles calculations and a deep potential machine learning method, along with our proposed potential energy difference approach, we discover that MPSnBr3, one type of organic-inorganic hybrid perovskite materials (OIHEMs), exhibits large reversible barocaloric effect (BCE) under RT conditions, with the isothermal entropy change (|ASrev|) and adiabatic temperature change (|ATrev|) reaching 105 J K-1 kg-1 and 43 K, respectively, along with a high coefficient of performance (COP) up to 4, which surpass the overall performance of most barocaloric materials. We unveil a ferroelectric phase transition mechanism through an analysis of the evolution of the dynamic process between the methylphosphonium (MP) organic molecules and the SnBr3 inorganic framework under different temperature and pressure. The giant BCE originates from a significant potential energy change across the pressure-induced phase transition, during which the vibrational entropy change (Svib) of the MP organic molecules contributes dominantly to the total entropy change. Moreover, pressure release facilitates the transfer of phonons from high frequency to low frequency, thereby enhancing the entropy of the system. The present work not only predicts superior barocaloric performance in OIHEMs but also provides important insights into the mechanism of tunable ferroelectric phase transition related to the BCE, which offers theoretical guidance for the design of novel materials for solid-state thermal management.

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