ferroelectricity

Ferroelectricity is a property of certain dielectric materials that exhibit spontaneous electric polarization, a built-in dipole moment per unit volume, which can be reversed by applying an external electric field. The polarization remains in the absence of a field (remanent polarization) and the response forms a hysteresis loop when the polarization is cycled, reflecting switchable domain orientations.

Most ferroelectrics are crystals with non-centrosymmetric structures that permit domain formation. The microscopic origin often involves off-center displacements of ions within the lattice, leading to a net polarization. As temperature changes, the material can undergo a phase transition to a paraelectric state with higher symmetry; the temperature at which spontaneous polarization vanishes is the Curie temperature (Tc).

Key parameters include spontaneous polarization (Ps), remanent polarization (Pr), and the coercive field (Ec) required to reverse polarization. Ferroelectrics typically also have large dielectric permittivity and strong coupling between electrical and mechanical states (piezoelectric effect), making domain wall motion important for switching dynamics.

Common ferroelectric materials include perovskites such as BaTiO3 and PbTiO3, and solid solutions like lead zirconate titanate (PZT). Ferroelectricity is a subset of pyroelectric and piezoelectric phenomena; all ferroelectrics are pyroelectric, but not all pyroelectrics are ferroelectric.

Applications span non-volatile memory (ferroelectric RAM), multilayer ceramic capacitors, actuators, sensors, and transducers. The field also explores lead-free alternatives due to environmental concerns and aims to understand domain behavior and aging/fatigue effects that influence long-term performance.