Electrostriction (cf.
magnetostriction
Magnetostriction (cf. electrostriction) is a property of magnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of materials' magnetization due to the applied magnetic field chang ...
) is a property of all electrical non-conductors, or
dielectrics
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mater ...
, that causes them to change their shape under the application of an
electric field
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field f ...
.
Explanation
Electrostriction is a property of all dielectric materials, and is caused by displacement of
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conv ...
s in the crystal lattice upon being exposed to an external electric field. 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 (elongation) in the direction of the field. The thickness will be reduced in the orthogonal directions characterized by
Poisson's ratio
In materials science and solid mechanics, Poisson's ratio \nu ( nu) is a measure of the Poisson effect, the deformation (expansion or contraction) of a material in directions perpendicular to the specific direction of loading. The value of Poi ...
. 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 (ratio of deformation to the original dimension) is proportional to the square of the
polarization
Polarization or polarisation may refer to:
Mathematics
*Polarization of an Abelian variety, in the mathematics of complex manifolds
*Polarization of an algebraic form, a technique for expressing a homogeneous polynomial in a simpler fashion by ...
. Reversal of the electric field does not reverse the direction of the deformation.
More formally, the electrostriction coefficient is a
fourth rank tensor
In mathematics, a tensor is an algebraic object that describes a multilinear relationship between sets of algebraic objects related to a vector space. Tensors may map between different objects such as vectors, scalars, and even other tenso ...
(
), relating the second-order strain tensor (
) and the first-order electric
polarization density
In classical electromagnetism, polarization density (or electric polarization, or simply polarization) is the vector field that expresses the density of permanent or induced electric dipole moments in a dielectric material. When a dielectric is ...
(
).
The related
piezoelectric effect
Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ''p ...
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
In geometry, a point group is a mathematical group of symmetry operations (isometries in a Euclidean space) that have a fixed point in common. The coordinate origin of the Euclidean space is conventionally taken to be a fixed point, and every p ...
. Electrostriction is a
quadratic effect, unlike piezoelectricity, which is a
linear
Linearity is the property of a mathematical relationship ('' function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear r ...
effect.
Materials
Although all dielectrics exhibit some electrostriction, certain engineered ceramics, known as
relaxor ferroelectric
Relaxor ferroelectrics are ferroelectric materials that exhibit high electrostriction. , although they have been studied for over fifty years, the mechanism for this effect is still not completely understood, and is the subject of continuing resea ...
s, have extraordinarily high electrostrictive constants. The most commonly used are
*
lead magnesium niobate
Lead magnesium niobate is a relaxor ferroelectric. It has been used to make piezoelectric microcantilever sensors.
References
Niobates
Magnesium compounds
Lead compounds
Piezoelectric materials
{{electromagnetism-stub ...
(PMN)
*
lead magnesium niobate-lead titanate
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...
(PMN-PT)
*
lead lanthanum zirconate titanate
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, l ...
(PLZT)
Magnitude of effect
Electrostriction can produce a strain of 0.1% at a field strength of 2 million volts per meter (2 MV/m) for the material called PMN-15 (TRS website listed in the references below). The effect appears to be quadratic at low field strengths (up to 0.3 MV/m) and roughly linear after that, up to a maximum field strength of 4 MV/m {{Citation needed, date=June 2010. Therefore, devices made of such materials are normally operated around a bias voltage in order to behave nearly linearly. This will probably cause deformations to lead to a change of electric charge, but this is unconfirmed.
Applications
*
Sonar projectors for submarines and surface vessels
*
Actuator
An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover".
An actuator requires a control device (controlled by control signal) an ...
s for small displacements
See also
*
Magnetostriction
Magnetostriction (cf. electrostriction) is a property of magnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of materials' magnetization due to the applied magnetic field chang ...
*
Photoelasticity
Photoelasticity describes changes in the optical properties of a material under mechanical deformation. It is a property of all dielectric media and is often used to experimentally determine the stress distribution in a material, where it gives ...
*
Piezomagnetism Piezomagnetism is a phenomenon observed in some antiferromagnetic and ferrimagnetic crystals. It is characterized by a linear coupling between the system's magnetic polarization and mechanical strain. In a piezomagnetic material, one may induce a s ...
*
Piezoelectricity
Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ' ...
*
Relaxor ferroelectric
Relaxor ferroelectrics are ferroelectric materials that exhibit high electrostriction. , although they have been studied for over fifty years, the mechanism for this effect is still not completely understood, and is the subject of continuing resea ...
References
"Electrostriction." Encyclopædia Britannica.* ''Mini dictionary of physics'' (1988) Oxford University Press
"Electrostrictive Materials"from TRS Technologies
by Prof. Dr. Helmut Föll
Materials science
Electric and magnetic fields in matter