In physics, the ferroelectric effect is an electrical phenomenon whereby certain ionic crystals may exhibit a spontaneous dipole moment. The term ferroelectricity refers to the similarity with ferromagnetism, in which a material exhibits a permanent magnetic moment.
There are two main types of ferroelectrics: displacive and order-disorder. The effect in barium titanate, a typical ferroelectric of the displacive type, is due to a polarization catastrophe, in which, if an ion is displaced from equilibrium slightly, the force from the local electric fields due to the ions in the crystal increase faster than the elastic restoring forces. This leads to an asymmetrical shift in the equilibrium ion positions and hence to a permanent dipole moment. In an order-disorder ferroelectric, there is a dipole moment in each unit cell, but at high temperatures they Ferroelectric effect are pointing in random directions. Upon lowering the temperature and going through the phase transition, the dipoles order, all pointing in the same direction within a domain.
Another important ferroelectric material is lead zirconate titanate.
Ferroelectric crystals often show several Curie points and domain structure hysteresis, much as do ferromagnetic crystals. By analogy to magnetic core memory, this hysteresis can be used to store information in ferroelectric RAM, which has ferroelectric capacitors as memory cells. The nature of the phase transition in some ferroelectric crystals is still not well understood.
Ferroelectrics often have very large dielectric constants, and thus are often found in capacitors. They also often have unusually large nonlinear optical coefficients.
Older publications used the term electret for ferroelectric materials.
See also
Physics
- Pyroelectricity
- Condensed matter physics
- Spintronics
- Ceramics
People
- Oliver Heaviside
Lists
- Examples of electrical phenomena
- List of physics topics
- List of electronics topics
Electronics Topics
The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. The design and construction of electronic circuits to solve practical problems is part of the fields of electronic engineering, and the hardware design side of computer engineering. The study of new semiconductor devices and their technology is sometimes considered as a branch of physics.
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