Ferroelectricity is a unique property exhibited by certain materials characterized by the spontaneous electric polarization that can be reversed or switched by an external electric field. These materials are called ferroelectric materials, and they exhibit a hysteresis loop in their polarization-electric field (P-E) curve, similar to the hysteresis loop observed in ferromagnetic materials.

Here are some key properties of ferroelectric materials:

1. Spontaneous Polarization: Ferroelectric materials have a spontaneous polarization that arises from the displacement of positive and negative charges within the material's crystal lattice, resulting in a net dipole moment even in the absence of an external electric field.

2. Polarization Reversibility: Ferroelectric materials can undergo a spontaneous reversal of polarization when subjected to an external electric field above a certain threshold known as the coercive field. This polarization reversal is reversible and can be repeated multiple times.

3. Hysteresis Behavior: The P-E curve of ferroelectric materials exhibits a hysteresis loop, similar to the magnetic hysteresis loop observed in ferromagnetic materials. This hysteresis behavior indicates that the polarization of the material depends not only on the current electric field but also on its history.

4. Curie Temperature: Ferroelectric materials exhibit their ferroelectric properties only below a certain temperature called the Curie temperature (Tc). Above the Curie temperature, the material loses its ferroelectric properties and becomes paraelectric.

5. Piezoelectricity: Many ferroelectric materials also exhibit piezoelectricity, a property where mechanical stress induces an electric polarization within the material, or conversely, an applied electric field causes mechanical deformation or strain. This property makes ferroelectric materials useful in applications such as sensors, actuators, and transducers.

6. Dielectric Permittivity: Ferroelectric materials have a high dielectric constant or permittivity, making them useful in capacitive devices such as capacitors and dielectric resonators.

7. Domain Structure: Ferroelectric materials consist of domains, regions within the material where the polarization vectors are aligned in a particular direction. Application of an electric field can cause domain switching, resulting in changes in the material's macroscopic polarization.

8. Ferroelectric Phase Transitions: Ferroelectric materials may undergo phase transitions between different ferroelectric phases, each characterized by different crystal structures and polarization properties.

Examples of ferroelectric materials include lead zirconate titanate (PZT), barium titanate (BaTiO3), lithium niobate (LiNbO3), and potassium dihydrogen phosphate (KDP). Ferroelectric materials find applications in various fields such as memory devices, sensors, actuators, piezoelectric transducers, ferroelectric capacitors, and non-volatile ferroelectric random access memory (FeRAM) devices.