Chapter:

ferroelectricity and piezoelectricity

Ferroelectricity: - Ferroelectric materials have a high dielectric constant, which is non-linear i.e., it depends to a considerable extent on the intensity of the electric field. Such materials exhibit hysterisis loops, i.e. the polarization is not a linear function of applied electric field. If the center of gravity of the positive and negative charges in a body does not coincide in the absence of an applied electric field, the substance has an electric dipole moment. So material is said to be spontaneously polarized and called ferroelectric material. Such a substance is called ferroelectric. It contains small regions called ferroelectric domains and all dipoles are parallely oriented in domain but different domains are randomly oriented in the absence of an external electric field. When the temperature exceeds a certain value called the Curie point, the substance loses its ferroelectric properties. Ex. Rochelle salt, Potassium dihydrogen phosphate, Barium titanate.

Piezoelectricity:- Piezoelectricity provides us a means of converting electrical energy to mechanical energy and vice versa.

When an electric field is applied to a substance it becomes polarized, the electrons and nuclei assume new geometric positions and the mechanical dimensions of the substance are altered. This phenomenon is called electrostriction. The reverse effect i.e. production of polarization by the application of mechanical stresses can take place only if the lattice has no centre of symmetry, this phenomenon is known as piezoelectricity. Ex. Rochelle salt, Quartz, Barium titanate.

Applications: Piezo electric materials serve as a source of ultrasonic waves. At sea they may be used.

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