electrostriction
/ ih-LEK-troh-STRIK-shun /
Put any insulating material in a strong electric field and it doesn't just polarize — it also changes shape, very slightly. As the field tugs the positive and negative charges in opposite directions and the molecules line up, the material squeezes or stretches by a tiny amount. This faint reshaping under a field, which happens in every dielectric, is electrostriction.
Unlike piezoelectricity, which only certain lopsided crystals show, electrostriction is universal — every dielectric does it, because pulling charges apart always slightly rearranges the spacing between atoms. The change in shape goes as the square of the field, which has a telling consequence: reversing the field's direction does not reverse the deformation. Whether you push the field one way or the other, the material strains the same way.
This matters because electrostrictive materials make precise, quiet actuators for things like fine-positioning stages and adaptive optics. The key contrast to remember: a piezoelectric crystal expands under one field direction and contracts under the reverse, so its motion tracks the field's sign, while an electrostrictive material always deforms the same way regardless of the field's sign. The honest caveat is that the effect is usually extremely small, so it only matters under strong fields or in specially tuned materials.
Certain electrostrictive ceramics are used as ultra-fine actuators in optical instruments: a changing voltage makes them expand by mere billionths of a meter, enough to nudge a mirror with exquisite precision. Reverse the voltage and they expand the very same way — a fingerprint that tells electrostriction apart from piezoelectricity.
An electrostrictive actuator deforms the same way no matter which way the voltage points.
Electrostriction occurs in every dielectric and is even in the field — reversing the field gives the same deformation — whereas piezoelectricity occurs only in non-symmetric crystals and reverses with the field.