It is a property of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field.
Some materials, known as paraelectric materials, show a more enhanced nonlinear polarization (see figure). The electric permittivity, corresponding to the slope of the polarization curve, is not constant as in dielectrics but is a function of the external electric field. The term is used in analogy to ferromagnetism, in which a material exhibits a permanent magnetic moment. Ferromagnetism was already known when ferroelectricity was discovered in 1920 in Rochelle salt by Valasek. A ferroelectric material is a material that exhibits, over some range of temperature, a spontaneous electric polarisation that can be reversed or reoriented by application of an electric field [poling]. Ferroelectric effect. The ferroelectric effect is an electrical phenomenon whereby certain crystals may exhibit a spontaneous dipole moment (which is called ferroelectric by analogy with ferromagnetic-exhibiting a permanent magnetic moment). The internal electric dipoles of a ferroelectric material are coupled to the material lattice so anything that changes the lattice will change the strength of the dipoles (in other words, a change in the spontaneous polarization). The change in the spontaneous polarization results in a change in the surface charge. The term is used in analogy to ferromagnetism, in which a material exhibits a permanent magnetic moment. Ferromagnetism was already known when ferroelectricity was discovered in 1920 in Rochelle salt by Valasek. Ferroelectricity is a property of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. The term is used in analogy to ferromagnetism, in which a material exhibits a permanent magnetic moment. Ferromagnetism was already known when ferroelectricity was discovered in 1920 in Rochelle salt by Valasek. It is an example of an improper ferroelectric material in which the phase transition from the paraelectric phase is controlled by the softening of a zone boundary mode, which would lead to a nonpolar low-temperature phase, which is in fact ferroelastic. Virtually all ferroelectric materials need to be electrically poled before use. In the case of LiTaO 3, silver electrodes are applied to faces perpendicular to the polar (c) axis and a pulsed field of about 10 V/cm (1 ms with a 50/50 duty cycle) applied while the crystal is cooled slowly through T C (620 °C). PZT is the most widely used ferroelectric material in industry as of 2011. It is a hybrid material between ferroelectric lead titanate and anti-ferroelectric lead zirconate, which allows formulas for the material to be engineered closer to one or the other ends of the ferroelectric or anti-ferroelectric spectrum. The ferroelectric effect draws its name from ferromagnetism, which describes permanent magnetic materials based on iron that are found in nature. This is a bit of a misnomer, however, as most ferroelectric materials are not based upon the element iron. Pyroelectricity (from the Greek pyr, fire, and electricity) is the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. Pyroelectricity should not be confused with thermoelectricity: In a typical demonstration of pyroelectricity, the whole crystal is changed from one temperature to another, and the result is a temporary voltage across the crystal. In a ferroelectric material, there is a net permanent dipole moment, which comes from the vector sum of dipole moments in each unit cell, σ μ. This means that it cannot exist in a structure that has a centre of symmetry, as any dipole moment generated in one direction would be forced by symmetry to be zero. Ferroelectric Materials. Note: DoITPoMS Teaching and Learning Packages are intended to be used interactively at a computer! This print-friendly version of the TLP is provided for convenience, but does not display all the content of the TLP. Ferroelectric materials are materials that possess a natural charge polarization that can be reversed by an external electric field, known as the process of switching. The ferroelectric effect draws its name from ferromagnetism, which describes permanent magnetic materials based on iron that are found in nature. This is a bit of a misnomer, however, as most ferroelectric materials are not based upon the element iron.
https://en.wikipedia.org/wiki/Ferroelectricity http://www.gitam.edu/eresource/Engg_Phys/semester_2/dielec/ferro.htm https://en.wikipedia.org/wiki/Ferroelectricity https://en.wikipedia.org/wiki/Ferroelectricity http://link.springer.com/referenceworkentry/10.1007/978-0-387-29185-7_27 http://www.wisegeek.com/what-are-ferroelectric-materials.htm https://en.wikipedia.org/wiki/Pyroelectricity http://www.doitpoms.ac.uk/tlplib/ferroelectrics/printall.php http://www.wisegeek.com/what-are-ferroelectric-materials.htm
what is ferroelectric material