TOPIC Ferroelectricity CLASS- M. Sc. 4 th sem. UNIT- 05, PAPER CODE- MPHYEC- 1B

Advanced Condensed Matter Physics

BY DR. RASHMI REKHA DEPARTMENT OF PHYSICS C. M. SCIENCE COLLEGE,DARBHANGA Discuss the different aspects ofofof Ferroelectricity

Ferroelectricity is a property of certain materials that have a spontaneous electric polarization. It can be reversed by the application of an external electric field .

The term is used in analogy to ferromagnetism, in which a material exhibits a permanent magnetic moment.

Ferroelectricity is named by analogy with ferro- magnetism, which occurs in such materials as iron. Iron atoms, being tiny magnets, spontaneously align themselves in clusters called ferromagnetic domains, which in turn can be oriented predominantly in a given direction by the application of an external magnetic field.

Behaviour ofofof Ferroelectric CrystalsCrystals: :::---- The ferroelectric hysteresis loop

This figure indicate the magnetic hysteresis hysteresis.. Because, the reverse of the orientation of the polarization direction by an electric field-Intrinsic Ferroelectricity. Polarization as a function of temperature

This figure indicates thermal disorder of the system i.e.,

T > Tc Variation of Er With T

This figure indicates the permittivity as the peak. Where

T=Tc Ferroelectric materialsmaterials: :::----

In this section some examples have been shown. For example, barium titanate (BaTiO3) and Rochelle salt are composed of crystals in which the structural units are tiny electric dipoles; that is, in each unit the centres of positive charge and of negative charge are slightly separated. In some crystals these electric dipoles spontaneously line up in clusters called domains, and in ferroelectric crystals the domains can be generated predominantly in one direction by a strong external electric field.

Reversing the external field reverses the predominant orientation of the ferroelectric domains, though the switching to a new direction lags somewhat behind the change in the external electric field. This lag of electric polarization behind the applied electric field is ferroelectric hysteresis named by analogy with ferromagnetic hysteresis .

Applications for Ferroelectric MaterialsMaterials: :::----

1. It is used in Capacitors.

2. It exhibits the properties of Non-volatile memory. 3. It is also used in Piezoelectrics for ultrasound imaging and actuators.

4. It is so important that it is used in Electro-optic materials for data storage applications.

5. Ferroelectricity is used in Switches, which is known as transchargers or transpolarizers.

6. It is also used in Oscillators and filters. 7. It is applicable for Light deflectors, modulators and displays.

Discussion :- Finally, we can say that Ferroelectricity ceases in a given material as a characteristic temperature, known as Curie tempurature. Due to the heat agitates the dipoles sufficiently to overcome the forces that spontaneously align them. ############# THANK YOU

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