Domains and Walls
A ferroelectric crystal freshly cooled through its Curie point breaks into a mosaic of domains — regions of uniform polarization separated by nanometer-thick walls. This domain structure minimizes the total energy: each domain reduces the depolarizing field, while domain walls cost surface energy. The equilibrium pattern balances these competing terms and depends on crystal shape, electrodes, and mechanical boundary conditions.
180-Degree Switching
When an electric field exceeds the coercive field, reversed domains nucleate — typically at electrodes, surfaces, or defect sites — and grow by the forward motion of 180-degree domain walls. The switching follows Kolmogorov-Avrami-Ishibashi (KAI) kinetics: initially slow (nucleation-limited), then rapid (growth-dominated), and finally slow again (impingement of growing domains). This simulator animates this process in real time.
90-Degree Switching and Strain
In tetragonal ferroelectrics like BaTiO3, the polarization can also rotate by 90 degrees into a perpendicular crystallographic axis. This 90-degree switching involves both electrical and mechanical changes — the unit cell elongates along the new polarization direction. The resulting macroscopic strain is the basis of piezoelectric actuation. In the simulation, 90-degree walls appear at 45-degree angles to the poling direction.
Pinning, Fatigue, and Aging
Real domain walls interact with crystal defects. Oxygen vacancies aggregate at wall positions, creating an internal bias field (imprint) that shifts the hysteresis loop. Repeated switching can cause fatigue — a progressive loss of switchable polarization as defect clusters grow at electrode interfaces. The wall mobility parameter in this simulator models the effective ease of wall motion through a defective lattice.