Phase transition and electrocaloric effect in PbZr_0.2Ti_0.8O₃thin films: insights from phase-field simulations

Ferroelectric (FE) ultrathin films tend to favor a homogeneous polar state at strong interfacial bound charge screening conditions. Reducing screening parameter (β) may induce topological textures such as vortices, labyrinth stripes, and skyrmion bubbles (sk-bs). Here, we exploreβ- and temperature-induced phase transitions of polarization reversal in FE PbZr_0.2Ti_0.8O₃(PZT) thin films using phase-field simulations under a 1% compressive strain. The results unveil a phase diagram comprising polarization reversal, hysteresis loop and topological structures. At room temperature, a phase transition from FE to antiferroelectric-like (AFE*) state occurs atβ∼0.53. At increasing temperatures, the FE and AFE* phases convert to a paraelectric state and form a tricritical point atβ∼0.78 andT∼ 770 K. Notably, at the phase boundary, a coexistence region of uniform polarization and isolated sk-bs emerges in a narrow screening range, which can be modulated by an applied electric field. Moreover, simulations of thermal effects on the FE to AFE* phase transition via the indirect method reveal a large electrocaloric effect around room temperature at low electric fields. Our findings uncover rich phenomena and elucidate underlying mechanisms in FE thin films, which hold promise for advanced device applications.