Materials Science > Electrical Properties > Ferroelectricity
Description:
Ferroelectricity is a property of certain materials characterized by the presence of a spontaneous electric polarization that can be reversed by the application of an external electric field. This phenomenon is closely analogous to ferromagnetism, which involves a permanent magnetic moment. Ferroelectric materials are a subset of pyroelectric and piezoelectric materials, which also exhibit related electrical phenomena.
In ferroelectric materials, the crystalline structure of the material enables electric dipoles to form and align in a coherent manner. These dipoles result in the formation of spontaneous electric polarization. The unique aspect of ferroelectricity is the ability to switch this polarization direction by applying an external electric field, which involves overcoming an energy barrier that separates different polarization states.
Mathematically, the relationship between polarization \(P\) and the electric field \(E\) in a ferroelectric material is typically described by a hysteresis loop. This can be illustrated succinctly with the equation:
\[ P(E) = P_r \pm P_s, \]
where \(P_r\) is the remnant polarization and \(P_s\) is the saturation polarization. When an increasing electric field is applied, the polarization increases up to a maximum value \(P_s\). When the electric field is removed, the material retains a remanent polarization \(P_r\). Reversing the direction of the electric field causes the polarization to switch, following a similar curve on the opposite side of the hysteresis loop.
The crystal structure most commonly associated with ferroelectricity is the perovskite structure, exemplified by materials such as barium titanate (BaTiO₃) and lead zirconate titanate (PZT). In these materials, the arrangement of ions within the unit cell underpins the spontaneous polarization and its switchable nature.
Ferroelectric materials have widespread applications in technology due to their unique properties. They are used in non-volatile memory devices (ferroelectric random access memory, FeRAM), piezoelectric sensors and actuators, capacitors, and other electronic components. Understanding and utilizing ferroelectricity is key to advances in many modern devices, particularly as the demand for more efficient and responsive electrical components grows.
Additionally, ferroelectricity often coexists with other phenomena like ferroelasticity and ferromagnetism in some materials, leading to multiferroicity, which represents a nexus of different ferroic orders in a single phase. Research into such materials is ongoing and aims to exploit the coupling between different types of order parameters for advanced multifunctional devices.
In summary, ferroelectricity is a fascinating electrical property found in certain materials that possess a spontaneous and reversible electric polarization. Its practical importance and intricate underlying physics make it a critical topic of study within materials science and electrical engineering.