Ferroelektriset

Ferroelectricity is a property of certain crystalline materials that exhibit a spontaneous electric polarization that can be reversed by the application of an external electric field. This spontaneous polarization is analogous to ferromagnetism, where materials have a spontaneous magnetic moment.

These materials possess a unique crystal structure that lacks a center of symmetry, allowing for a permanent electric dipole moment. When these dipoles align within domains, the material as a whole exhibits a net polarization. The direction of this polarization can be switched by applying an electric field in the opposite direction. This switching behavior is characteristic of ferroelectric materials and is responsible for their technological applications.

The relationship between the electric polarization (P) and the electric field (E) in ferroelectric materials is non-linear and exhibits hysteresis. When an electric field is applied and then removed, the polarization does not return to zero but retains a residual polarization, known as remanent polarization. To reduce the polarization to zero, a reverse electric field, called the coercive field, must be applied.

Ferroelectric materials are important in various electronic devices. Their ability to store and switch polarization makes them suitable for non-volatile memory applications, such as ferroelectric random-access memory (FeRAM). They are also used in sensors, actuators, and microwave devices due to their piezoelectric and pyroelectric properties, which are often present in ferroelectric materials. Common examples of ferroelectric materials include barium titanate (BaTiO3) and lead zirconate titanate (PZT).