Local 90° switching in Pb(Zr_0.2Ti_0.8)O ₃ thin film: Phase-field modeling

Polarization switching under an applied electrical field is a fundamental property of ferroelectric materials and has been explored for ferroelectric memory and electromechanical sensor applications. Ferroelectric/ferroelastic Pb(Zr_0.2Ti_0.8)O₃ (PZT) epitaxial thin films have been extensively studied due to their high electromechanical responses. Herein, we study the switching kinetics of PZT thin films under a local applied bias simulating a piezoresponse force microscopy tip via the phase-field approach. Local 90° switching was observed along with 180° switching, in good agreement with previous experimental observations. Different switching patterns are observed at different applied bias for films under different substrate strains. Generally, under low to medium bias, 90° switching is favored due to the huge release of elastic energy. While under a high applied bias, 180° switching dominates with large electrostatic energy decrease. It is worthwhile noting that the less mobile 90° domain wall cannot be fully switched back by a reverse electric field, which could lead to the "fatigue behavior".