Electrostriction
In electromagnetism, electrostriction is a property of all electrical non-conductor or dielectrics. Electrostriction causes these materials to change their shape under the application of an electric field. It is the dual property to magnetostriction.
Explanation
Electrostriction is a property of all dielectric materials, and is caused by displacement of ions in the crystal lattice upon being exposed to an external electric field. The cause of electrostrictive is linked to anharmonic effects. Positive ions will be displaced in the direction of the field, while negative ions will be displaced in the opposite direction. This displacement will accumulate throughout the bulk material and result in an overall strain in the direction of the field. The thickness will be reduced in the orthogonal directions characterized by Poisson's ratio. All insulating materials consisting of more than one type of atom will be ionic to some extent due to the difference of electronegativity of the atoms, and therefore exhibit electrostriction.The resulting strain is proportional to the square of the polarization. Reversal of the electric field does not reverse the direction of the deformation.
More formally, the electrostriction coefficient is a rank four tensor, relating the rank two strain tensor and the electric polarization density vector
The electrostrictive tensor satisfies
The related piezoelectric effect occurs only in a particular class of dielectrics. Electrostriction applies to all crystal symmetries, while the piezoelectric effect only applies to the 20 piezoelectric point groups. Piezoelectricity is equivalent to the electrostrictive displacement of ions in ferroelectric materials. Electrostriction is a quadratic effect, unlike piezoelectricity, which is a linear effect.