ferroelectric

Ferroelectricity is the property of certain materials to exhibit spontaneous electric polarization that can be reversed by an external electric field. This polarization exists without an applied field due to a noncentrosymmetric crystal structure and often forms domains whose orientation can be reconfigured by switching fields. The phenomenon is temperature dependent, with a Curie temperature at which a material transitions to a paraelectric phase in which spontaneous polarization disappears and dielectric behavior changes markedly.

Key characteristics include a hysteresis loop in polarization versus electric field, a remanent polarization, and a coercive field. Ferroelectrics are typically insulators with high dielectric constants, and most exhibit piezoelectric and pyroelectric properties as a consequence of their polar structure. Above the Curie temperature they become paraelectric and lose spontaneous polarization.

Many well-known ferroelectrics are perovskites, such as barium titanate (BaTiO3), lead titanate (PbTiO3), and solid solutions like lead zirconate titanate (PZT). Classic ferroelectrics include Rochelle salt, and broader classes encompass polymer ferroelectrics such as polyvinylidene fluoride (PVDF). The microscopic mechanism often involves off-center displacement of ions within the crystal lattice, leading to a net dipole moment.

Applications span nonvolatile memories (FeRAM), capacitors with large permittivity, actuators, sensors, energy harvesting devices, and electro-optic components. Ferroelectric materials also present challenges, including fatigue, aging, and issues related to lead content in some compounds.