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

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.