Field-Induced Antiferroelectric–Ferroelectric Transformation in Organometallic Perovskite Displaying Giant Negative Electrocaloric Effect
Shiguo Han, Jie Bie, Wei Fa, Shuang Chen, Liwei Tang, Wuqian Guo, Haojie Xu, Yu Ma, Yi Liu, Xitao Liu, Zhihua Sun, Junhua Luo
Abstract
Antiferroelectric materials with an electrocaloric effect (ECE) have been developed as promising candidates for solid-state refrigeration. Despite the great advances in positive ECE, reports on negative ECE remain quite scarce because of its elusive physical mechanism. Here, a giant negative ECE (maximum Δ S ∼ −33.3 J kg –1 K –1 with Δ T ∼ −11.7 K) is demonstrated near room temperature in organometallic perovskite, i BA 2 EA 2 Pb 3 I 10 ( 1, where i BA = isobutylammonium and EA = ethylammonium), which is comparable to the greatest ECE effects reported so far. Moreover, the ECE efficiency Δ S /Δ E (∼1.85 J cm kg –1 K –1 kV –1 ) and Δ T /Δ E (∼0.65 K cm kV –1 ) are almost 2 orders of magnitude higher than those of classical inorganic ceramic ferroelectrics and organic polymers, such as BaTiO 3, SrBi 2 Ta 2 O 9, Hf 1/2 Zr 1/2 O 2, and P(VDF-TrFE). As far as we know, this is the first report on negative ECE in organometallic hybrid perovskite ferroelectric. Our experimental measurement combined with the first-principles calculations reveals that electric field-induced antipolar to polar structural transformation results in a large change in dipolar ordering (from 6.5 to 45 μC/cm 2 under the Δ E of 18 kV/cm) that is closely related to the entropy change, which plays a key role in generating such giant negative ECE. This discovery of field-induced negative ECE is unprecedented in organometallic perovskite, which sheds light on the exploration of next-generation refrigeration devices with high cooling efficiency.