The coexistence of the negative and positive electrocaloric effect (ECE) caused by an applied electric field direction different from the dipole direction of 180 • domain structures is firstly found in ferroelectric thin films using the phase-field-based simulation. The calculation results reveal that a negative adiabatic temperature change (∆T = −3.4 K) and a positive adiabatic temperature change (∆T = 3.1 K) coexist in the PbTiO3 thin film with 180 • domain structures under the dimensional electric field ∆E = 0.1. The coexistence of negative and positive ECE in a thin film can provide a new way to design solid-state refrigerators.

Barium zirconate titanate (BZT) (Ba(ZrTi)O) ceramics with Zr contents of x = 5, 10, 15, 20, 25, and 30 mol % were prepared using a solid-state reaction approach. The microstructures, morphologies, and electric properties were characterized using X-ray diffraction, scanning electron microscopy, and impedance analysis methods, respectively. The dielectric analyses indicate that the BZT bulk ceramics show characteristics of phase transition from a normal ferroelectric to a relaxor ferroelectric with the increasing Zr ionic content. The electrocaloric effect adiabatic temperature change decreases with the increasing Zr content. The highest adiabatic temperature change obtained is 2.4 K for BZT ceramics with a 5 mol % of Zr ionic content.

The influence of vortex domain switching on the electrocaloric (EC) property of a PbTiO 3 nanoparticle is studied using the phase field method combined with thermodynamics analysis. The calculation results reveal that both a very large negative adiabatic temperature change (DT ¼ À6.34 K) and a positive adiabatic temperature change (DT ¼ 4.16 K) appear in the PbTiO 3 nanoparticle when the vortex domain switches from the clockwise state to the counterclockwise state under a curled electric field. The obtained results will be of help in understanding the EC property in ferroelectrics with multidomain structure.

Electrocaloric effects of Bi 4 Ti 3 O 12 (BIT) ferroelectric nanoparticles with vortex domain structures in a curled electric field are investigated using a phase field method. A large adiabatic temperature change (DT = 16.6 K) is observed in the BIT nanoparticles with the change in vorticity vector of the curled field DQ = 0.15 mV Å 22 at 620 uC. This large DT is attributed to a large change in the toroidal moment which is associated with vortex domain structures in the nanoparticles under the curled electric field. These results indicate that ferroelectric nanostructures with vortex domain structures can be exploited for use in solid state refrigeration.

Barium strontium zirconate titanate ceramics ((BaSr)(ZrTi)O 3 -BSZT) with Zr 4+ ionic contents of 15 and 20 mol % and Sr 2+ ionic contents of 15, 20, 25, and 30 mol % were prepared using a solid-state reaction approach. X-ray diffraction and scanning electron microscopy were used to characterize the lattice structure and morphologies of the ceramics. Permittivity and polarization as a function of temperature were characterized using an impedance analyzer and a Tower−Sawyer circuit. The electrocaloric effect was measured directly and calculated using the Maxwell relation (indirectly). The results indicated that the BSZT ceramics change from a normal ferroelectric to a relaxor ferroelectric with increasing Zr 4+ ionic content, which can be further modified by the addition of Sr 2+ ionic content. The optimized adiabatic temperature change ΔT obtained is 2.43 K in (Ba 0.85 Sr 0.15 )(Zr 0.15 Ti 0.75 )O 3 ceramics, and ΔT >1.6 K over a wide temperature span of 120 °C was obtained.