中国科学院福建物构所孙志华团队开发了一种在接近室温下仍具有巨大电热强度的软钙钛矿型反铁电体。 该项研究成果发表在2020年11月23日出版的《美国化学会志》上。

反铁电材料具有与相邻偶极子的反平行排列特征，由于其电致热效应，在固体制冷领域具有广阔的应用前景。尽管无机氧化物和一些有机软质聚合物取得了很大的进展，但它们的电致热（EC）效应是在较高的电场下实现的，这导致其在实际应用中的EC强度太低。目前，开发具有较强EC强度的软反铁电体是一个挑战。

通过混合离子合金化，研究人员开发了一种新的钙钛矿型软反铁电体（isopentylammonium）2CsPb2Br7（1），它同时包含有机间隔阳离子和无机钙钛矿化剂Cs+部分。值得注意的是，在321 K和350K下，有机间隔剂的重取向与Cs+离子的原子位移之间的协同作用触发了其多次铁电-反铁电-顺电相变。通过对自然极化和电场迟滞回线表征，确定铁电和反铁电分别是1阶。在13kV/cm的低电场下，反铁电相中反极偶极子在1阶重排使其具有15.4 K m MV–1的巨大近室温EC强度（ΔTEC/ΔE）。这一优点与BaTiO3（约16K m/MV）的最高值不相上下，但远远超过了最先进的软聚合物。1的潜在EC机制归因于极低的开关偶极子的临界场，包括有机间隔剂的重新定向和Cs+阳离子的移动。此外，显著的EC熵变（～4.1 J K–1 kg–1）和温度变化（～2K）揭示了1的固态制冷潜力。

这种近室温EC强度的发现在混合钙钛矿家族中是史无前例的，它为探索新的软反铁电材料在高效制冷装置上的应用提供了方向。

附：英文原文

Title: Soft Perovskite-Type Antiferroelectric with Giant Electrocaloric Strength near Room Temperature

Author: Maofan Li, Shiguo Han, Yi Liu, Junhua Luo, Maochun Hong, Zhihua Sun

Issue&Volume: November 23, 2020

Abstract: Antiferroelectric materials, characterized by an antiparallel array of adjacent dipoles, are holding a bright future for solid-state refrigeration based on their electrocaloric (EC) effects. Despite great advances of inorganic oxides and some organic soft polymers, their EC effects are achieved under quite high electric fields that result in too low EC strengths for practical application. Currently, it is a challenge to exploit soft antiferroelectric with strong EC strengths. Here, by the mixed-cation alloying, we present a new perovskite-type soft antiferroelectric, (isopentylammonium)2CsPb2Br7 (1), which incorporates both an organic spacing cation and an inorganic perovskitizer Cs+ moiety. Remarkably, the synergic cooperativity between the reorientation of the organic spacer and atomic displacement of Cs+ cation triggers its multiple ferroelectric–antiferroelectric–paraelectric phase transitions at 321 and 350 K. Their natural polarization vs electric field hysteresis loops are characterized to confirm ferroelectric and antiferroelectric orders of 1, respectively. It is emphasized that, under a low electric field of 13 kV/cm, the antipolar dipole realignment in 1 endows a giant near-room-temperature EC strength (ΔTEC/ΔE) of 15.4 K m MV–1 at antiferroelectric phase. This merit is on par with the record-high value of BaTiO3 (～16 K m/MV) but far beyond the state-of-the-art soft polymers. The underlying EC mechanism for 1 is ascribed to the extremely low critical field to switch dipoles, involving the reorientation of the organic spacer and the shift of the Cs+ cation. Besides, notable EC entropy change (～4.1 J K–1 kg–1) and temperature change (～2 K) reveal potentials of 1 for solid-state refrigeration. As far as we know, this discovery of near-room-temperature EC strengths is unprecedented in the hybrid perovskite family, which sheds light on the exploration of new soft antiferroelectrics toward high-efficiency refrigeration devices.

DOI: 10.1021/jacs.0c09601

Source: https://pubs.acs.org/doi/10.1021/jacs.0c09601