Giant room temperature electrocaloric effect in a layered hybrid perovskite ferroelectric: [(CH3)2CHCH2NH3]2PbCl4

Abstract

Electrocaloric effect driven by electric fields displays great potential in realizing highly efficient solid-state refrigeration. Nevertheless, most known electrocaloric materials exhibit relatively poor cooling performance near room temperature, which hinders their further applications. The emerging family of hybrid perovskite ferroelectrics, which exhibits superior structural diversity, large heat exchange and broad property tenability, offers an ideal platform. Herein, we report an exceptionally large electrocaloric effect near room temperature in a designed hybrid perovskite ferroelectric [(CH₃)₂CHCH₂NH₃]₂PbCl₄, which exhibits a sharp first-order phase transition at 302 K, superior spontaneous polarization (>4.8 μC/cm²) and relatively small coercive field (<15 kV/cm). Strikingly, a large isothermal entropy change ΔS of 25.64 J/kg/K and adiabatic temperature change ΔT of 11.06 K under a small electric field ΔE of 29.7 kV/cm at room temperature are achieved, with giant electrocaloric strengths of isothermal ΔS/ΔE of 0.86 J·cm/kg/K/kV and adiabatic ΔT/ΔE of 370 mK·cm/kV, which is larger than those of traditional ferroelectrics. This work presents a general approach to the design of hybrid perovskite ferroelectrics, as well as provides a family of candidate materials with potentially prominent electrocaloric performance for room temperature solid-state refrigeration.

Fig. 1. Illustration of phase transitions of 1.

a Monoclinic phase at 285 K. b Orthorhombic phase at 318 K. c Orthorhombic phase at 343 K.

Fig. 2. Phase transitions in 1.

a Top panel, heat flow dQ/dT on heating (red) and cooling (blue) across the FE–PE transition. Bottom panel, the resulting temperature dependence entropy change ΔS. b Temperature-dependent relative permittivities. Inset is the temperature-dependent dielectric loss (tan δ).

Fig. 3. Physical properties related to phase transition and symmetry breaking.

a Temperature-dependent spontaneous polarization obtained from the integration of pyroelectric current. Inset: pyroelectric current measured with temperature increasing. b Temperature-dependent SHG response.

Fig. 4. Ferroelectric and EC performance.

a Polarization versus electric field characteristics measured at different temperatures. b Temperature-dependent polarization at different electric fields, extracted from (a). c Temperature-dependent adiabatic temperature change ΔT at different ΔE. d Temperature-dependent isothermal entropy changes ΔS at different ΔE. e Comparison in terms of cooling performance between 1 and a number of known EC materials.

Fig. 5. Ab initio calculated EC performance.

The EC entropy change ΔS (a) and the EC temperature change ΔT (b) for 1 under different electric field changes.