Large Low-Field-Driven Electrocaloric Effect in Organic-Inorganic Hybrids

Due to environmental-friendliness and high-efficiency, electrocaloric effect (ECE) is widely regarded as a refrigeration technology for tomorrow [1-7]. An ideal electrocaloric material should possess a low driving field and a giant entropy change. However, the currently focused materials, i.e. organic PVDF-based polymers and inorganic ceramics, possess their own bottleneck. The polar-chain flipping polarization grants organic PVDF-based polymers a colossal entropy change of 100 J×kg^-1×K^-1 albeit an extremely-high driving field of ~ 100 MV×m^-1 [4,5] while most inorganic perovskites exhibit a low driving field below 10 MV×m^-1 but a much smaller entropy change below 10 J×kg^-1×K^-1 [6,7]. Herein, utilizing organic-inorganic hybridization strategy integrating the large entropy change of organic polymers and the low driving field of inorganic ceramics, a record low-field-driven ECE of 33.1 J×kg^-1×K^-1 @ 7.3 MV×m^-1 and a record directly measured electrocaloric strength (ECS) of 5.64 J×kg^-1×K^-1×MV^-1×m were achieved in organic-inorganic hybrids. Single-crystal X-ray diffraction combined with Raman Spectra revealed that the simultaneous order-disorder transition of organic part and dramatic structure change of inorganic part are responsible for the giant ECE. Moreover, DFT calculations conveyed that the unique electric-field-induced metastable phase and consequential two-step meta-electric transition could lower the transition energy barrier and account for the low driving field. This work provides a new way for designing high-performance electrocaloric materials via organic-inorganic hybridization.

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