Negative/Positive Electrocaloric Effect in Single-Layer Pb(ZrₓTi1–x)O₃ Thin Films for Solid-State Cooling Device

Ferroelectric perovskite materials are crucial candidates for the solid-state cooling devices due to their distinguished electrocaloric effect (ECE). Here we report the coexistence of negative and positive ECE in sol-gel derived single-layer (SL) Pb(Zr
_x
Ti
_1-x
)O
₃
(PZT) thin films with a composition close to the morphotropic phase boundary (MPB). A negative ECE of ΔT = -1.81 K at 135 °C and positive ECE of ΔT = 0.64 K at 40 °C under an applied electric field of 374 kV cm
^-1
are achieved. Such appearance of negative and positive ECE at different temperatures is attributed to the transition from rhombohedral to tetragonal phase and associated with the effect of defect dipoles in SL-PZT thin films at MPB.