Ferroics
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In physics, ferroics is the study of ferromagnets, ferroelectrics, and ferroelastics.
In physics, ferroics is the study of ferromagnets, ferroelectrics, and ferroelastics.
Phase transitions
The basis of ferroics is to understand large changes in physical characteristics that can occur over a narrow temperature range. Changes in physical characteristics occur when phase transitions take place around some critical temperature value, normally denoted by T_c . Above this critical temperature, the crystal is in a nonferroic state and does not exhibit ferroic characteristics. Falling below T_c it undergoes a spontaneous phase transition. Such a transition typically results in a small deviation from the nonferroic crystal structure, but with a different shape of the unit cell, the point symmetry of the material is reduced. This breaking of symmetry allows the formation of the ferroic phase. Lowering the temperature below T_c includes a spontaneous dipole moment along an axis of the unit cell. Although individual dipole moments can sometimes be small, the effect of 10^{24} unit cells gives rise to a significant electric field. Ferroelectrics cannot exist in a centrosymmetric crystal. A centrosymmetric crystal is one where lattice point \left (x,y,z \right ) can be mapped onto lattice point \left ( -x,-y,-z \right ) . The spontaneous magnetization of a ferromagnet can be attributed to a breaking of point symmetry in switching from the paramagnetic to the ferromagnetic phase. In this case, T_c is known as the Curie temperature. In ferroelastic crystals, in going from the nonferroic (or prototypic phase) to the ferroic phase, a spontaneous strain is induced. An example of a ferroelastic phase transition is when the crystal structure spontaneously changes from a tetragonal structure (a square prism shape) to a monoclinic structure (a general parallelepiped). Here the shapes of the unit cell before and after the phase transition are different, inducing a strain within the material.
See also
Piezoelectricity Pyroelectricity
References
Text derived from https://en.wikipedia.org/w/index.php?oldid=1362973336 under CC BY-SA 4.0; modifications have been made.