Ferroelectricityssä

Ferroelectricity is a property exhibited by certain dielectric materials that possess a spontaneous electric polarization which can be reversed by the application of an external electric field. This phenomenon is analogous to ferromagnetism, where materials exhibit spontaneous magnetization that can be switched by a magnetic field, hence the term "ferroelectric." The term was coined by Woldemar Voigt in 1921, though the effect was first observed in 1920 by Valasek in Rochelle salt (sodium potassium tartrate tetrahydrate).

Ferroelectric materials are typically crystalline and exhibit a phase transition between a paraelectric phase (above the Curie temperature) and a ferroelectric phase (below the Curie temperature). In the ferroelectric phase, the material's unit cell exhibits a net dipole moment due to the displacement of ions or atoms from their centrosymmetric positions. This polarization can be switched between two or more stable states by applying an electric field, making ferroelectric materials useful in memory storage devices, sensors, and actuators.

Key characteristics of ferroelectric materials include:

- Spontaneous polarization in the absence of an external electric field.

- The ability to switch polarization direction with an applied electric field.

- Hysteresis in the polarization-electric field loop, similar to the magnetization-magnetic field loop in ferromagnetic materials.

- Existence of a Curie temperature, above which the material loses its ferroelectric properties and becomes paraelectric.

Common ferroelectric materials include barium titanate (BaTiO₃), lead zirconate titanate (PZT), and lithium niobate (LiNbO₃). These materials are widely used in capacitors, non-volatile memory (such as ferroelectric random-access memory, or FeRAM), piezoelectric transducers, and pyroelectric sensors. Ferroelectricity also plays a role in multiferroic materials, which combine ferroelectricity with other ordering phenomena like ferromagnetism or ferroelasticity. Research in ferroelectric materials continues to explore new compounds and applications, including those in energy harvesting, photonics, and quantum computing.