Information about Ferroelectric
Ferroelectricity is a physical property of a material whereby it exhibits a spontaneous electric dipole moment, the direction of which can be switched between equivalent states by the application of an external electric field. Ferroelectrics are key materials in microelectronics. Their excellent dielectric properties make them suitable for electronic components such as capacitors, filters etc.
Older publications used the term electret for ferroelectric materials.
The combined properties of memory, piezoelectricity, and pyroelectricity make ferroelectric capacitors some of the most useful technological devices in modern society. Ferroelectric capacitors are at the heart of medical ultrasound machines (the capacitors generate and then listen for the ultrasound "ping" used to image the internal organs of a body), high quality infrared cameras (the infrared image is projected onto a two dimensional array of ferroelectric capacitors capable of detecting temperature differences as small as millionths of a degree Celsius), fire sensors, sonar, vibration sensors, and even fuel injectors on diesel engines. Engineers use the high dielectric constants of ferroelectric materials to concentrate large values of capacitance into small volumes, resulting in the very tiny surface mount capacitor. Without the space savings allowed by surface mount capacitors, compact laptop computers and cell phones simply would not be possible. As well, the electro-optic modulators that form the backbone of the Internet are made with ferroelectric materials.
A ferroelectric tunnel junction (FTJ) is a contact made up by nanometer-thick ferroelectric film placed between metal electrodes. The thickness of the ferroelectric layer is thin enough to allow tunneling of electrons. The piezoelectric and interface effects as well as the depolarization field may lead to a giant electroresistance (GER) switching effect.
Another important ferroelectric material is lead zirconate titanate.
Ferroelectric crystals often show several transition temperatures and domain structure hysteresis, much as do ferromagnetic crystals. The nature of the phase transition in some ferroelectric crystals is still not well understood.
The ferroelectric effect also finds use in liquid crystal physics by incorporation of a chiral dopant into an achiral smectic C matrix. These liquid crystals exhibit the Clark-Lagerwall effect[1] which effects a change in one bistable state to another upon switching of electric field direction.
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Older publications used the term electret for ferroelectric materials.
History
The term ferroelectricity is used in analogy to ferromagnetism, in which a material exhibits a permanent magnetic moment. Ferromagnetism was already known when ferroelectricity was discovered in the late 1800s. Thus, the prefix "ferro", meaning iron, was used to describe the property despite that fact that most ferroelectric materials do not have iron in their lattice.Applications
Placing a ferroelectric material between two conductive plates creates a ferroelectric capacitor. Ferroelectric capacitors exhibit nonlinear properties and usually have very high dielectric constants. The fact that the internal electric dipoles can be forced to change their direction by the application of an external voltage gives rise to hysteresis in the "polarization vs voltage" property of the capacitor. In this case, polarization is defined as the total charge stored on the plates of the capacitor divided by the area of the plates. Hysteresis means memory and ferroelectric capacitors are used to make ferroelectric RAM for computers and RFID cards.The combined properties of memory, piezoelectricity, and pyroelectricity make ferroelectric capacitors some of the most useful technological devices in modern society. Ferroelectric capacitors are at the heart of medical ultrasound machines (the capacitors generate and then listen for the ultrasound "ping" used to image the internal organs of a body), high quality infrared cameras (the infrared image is projected onto a two dimensional array of ferroelectric capacitors capable of detecting temperature differences as small as millionths of a degree Celsius), fire sensors, sonar, vibration sensors, and even fuel injectors on diesel engines. Engineers use the high dielectric constants of ferroelectric materials to concentrate large values of capacitance into small volumes, resulting in the very tiny surface mount capacitor. Without the space savings allowed by surface mount capacitors, compact laptop computers and cell phones simply would not be possible. As well, the electro-optic modulators that form the backbone of the Internet are made with ferroelectric materials.
A ferroelectric tunnel junction (FTJ) is a contact made up by nanometer-thick ferroelectric film placed between metal electrodes. The thickness of the ferroelectric layer is thin enough to allow tunneling of electrons. The piezoelectric and interface effects as well as the depolarization field may lead to a giant electroresistance (GER) switching effect.
Materials
The internal electric dipoles of a ferroelectric material are physically tied to the material lattice so anything that changes the physical lattice will change the strength of the dipoles and cause a current to flow into or out of the capacitor even without the presence of an external voltage across the capacitor. Two stimuli that will change the lattice dimensions of a material are force and temperature. The generation of a current in response to the application of a force to a capacitor is called piezoelectricity. The generation of current in response to a change in temperature is called pyroelectricity. 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 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 transition temperatures and domain structure hysteresis, much as do ferromagnetic crystals. The nature of the phase transition in some ferroelectric crystals is still not well understood.
The ferroelectric effect also finds use in liquid crystal physics by incorporation of a chiral dopant into an achiral smectic C matrix. These liquid crystals exhibit the Clark-Lagerwall effect[1] which effects a change in one bistable state to another upon switching of electric field direction.
See also
Stabilizing ferroelectric materialsPhysics
People
Lists
References
1. ^ Noel A. Clark, Sven Torbjörn Lagerwall: Submicrosecond Bistable Electro-Optic Switching in Liquid Crystals, Appl. Phys. Lett. 36, 899 (1980)
External links
Dipole moment refers to the quality of a system to behave like a dipole. This could be:
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- Electrical dipole moment, the measure of the electrical polarity of a system of charges
- Magnetic dipole moment, the measure of the magnetic polarity of a system of charges
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Electret (formed of elektr- from "electricity" and -et from "magnet") is a dielectric material that has a quasi-permanent electric charge or dipole polarisation.
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Ferromagnetism is the "normal" form of magnetism with which most people are familiar, as exhibited in horseshoe magnets and refrigerator magnets, for instance. It is responsible for most of the magnetic behavior encountered in everyday life.
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In physics, the magnetic moment or magnetic dipole moment is a measure of the strength of a magnetic source. In the simplest case of a current loop, the magnetic moment is defined as:
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Ferroelectric capacitor is a capacitor used in digital electronics as a component of ferroelectric RAM, a type of non-volatile computer memory.
In a ferroelectric capacitor, the dielectric layer is replaced with a thin ferroelectric film, typically made of lead zirconate
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In a ferroelectric capacitor, the dielectric layer is replaced with a thin ferroelectric film, typically made of lead zirconate
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nonlinear system is a system which is not linear i.e. a system which does not satisfy the superposition principle. Less technically, a nonlinear system is any problem where the variable(s) to be solved for cannot be written as a linear sum of independent components.
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The relative static permittivity (or static relative permittivity) of a material under given conditions is a measure of the extent to which it concentrates electrostatic lines of flux.
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A system with hysteresis exhibits path-dependence, or "rate-independent memory". Consider a deterministic system with no hysteresis and no dynamics. In that case, we can predict the output of the system at some instant in time, given only the input to the system at that instant.
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Ferroelectric RAM (FeRAM or FRAM[1]) is a type of non-volatile computer memory. It is similar in constructionDRAM, which is currently used in the majority of a computer's main memory, but uses a ferroelectric layer to achieve non-volatility.
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Radio-frequency identification (RFID) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders.
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Piezoelectricity is the ability of some materials (notably crystals and certain ceramics) to generate an electric potential[1] in response to applied mechanical stress. This may take the form of a separation of electric charge across the crystal lattice.
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Pyroelectricity is the ability of certain materials to generate an electrical potential when they are heated or cooled. As a result of this change in temperature, positive and negative charges move to opposite ends through migration (i.e.
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Electro-optic modulator (EOM) is an optical device in which a signal-controlled element displaying electro-optic effect is used to modulate a beam of light. The modulation may be imposed on the phase, frequency, amplitude, or direction of the modulated beam.
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Piezoelectricity is the ability of some materials (notably crystals and certain ceramics) to generate an electric potential[1] in response to applied mechanical stress. This may take the form of a separation of electric charge across the crystal lattice.
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Pyroelectricity is the ability of certain materials to generate an electrical potential when they are heated or cooled. As a result of this change in temperature, positive and negative charges move to opposite ends through migration (i.e.
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Barium titanate is an oxide of barium and titanium with the chemical formula BaTiO3. It is a ferroelectric ceramic material, with a photorefractive effect and piezoelectric properties.
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electric field. This electric field exerts a force on other electrically charged objects. The concept of electric field was introduced by Michael Faraday.
The electric field is a vector field with SI units of newtons per coulomb (N C−1
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The electric field is a vector field with SI units of newtons per coulomb (N C−1
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In physics, force is an action or agency that causes a body of mass m to accelerate. It may be experienced as a lift, a push, or a pull. The acceleration of the body is proportional to the vector sum of all forces acting on it (known as net force or resultant force).
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Lead zirconate titanate (Pb[ZrxTi1-x]O3 0<x
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CRYSTAL is a quantum chemistry ab initio program, designed primarily for calculations on crystals (3 dimensions), slabs (2 dimensions) and polymers (1 dimension) using translational symmetry, but it can be used for single molecules.[1] It is written by V.R. Saunders, R.
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Ferromagnetism is the "normal" form of magnetism with which most people are familiar, as exhibited in horseshoe magnets and refrigerator magnets, for instance. It is responsible for most of the magnetic behavior encountered in everyday life.
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phase transition or phase change is the transformation of a thermodynamic system from one phase to another. The distinguishing characteristic of a phase transition is an abrupt change in one or more physical properties, in particular the heat capacity, with a small change in
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Liquid crystals are substances that exhibit a phase of matter that has properties between those of a conventional liquid, and those of a solid crystal. For instance, a liquid crystal (LC) may flow like a liquid, but have the molecules in the liquid arranged and/or oriented in a
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Paraelectricity occurs in crystal phases in which electric dipoles are unaligned (i.e. unordered domains that are electrically charged) and thus have the potential to align in an external electric field and strengthen it.
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Piezoelectricity is the ability of some materials (notably crystals and certain ceramics) to generate an electric potential[1] in response to applied mechanical stress. This may take the form of a separation of electric charge across the crystal lattice.
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Pyroelectricity is the ability of certain materials to generate an electrical potential when they are heated or cooled. As a result of this change in temperature, positive and negative charges move to opposite ends through migration (i.e.
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Condensed matter physics is the field of physics that deals with the macroscopic physical properties of matter. In particular, it is concerned with the "condensed" phases that appear whenever the number of constituents in a system is extremely large and the interactions
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Spintronics (a neologism for "spin-based electronics"), also known as magnetoelectronics, is an emerging technology which exploits the quantum spin states of electrons as well as making use of their charge state.
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ceramic is derived from the Greek word κεραμικός (keramikos). The term covers inorganic non-metallic materials which are formed by the action of heat.
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