Qualitative explanation of hysteresis loop

In the last article, I have discussed about ferroelectricity and hysteriesis loop. Today we will discuss about the reason of hysteresis loop.

Ferroelectric crystals have regions with uniform polarization called ferroelectric domains.

A single crystal of ferroelectric material may contain number of domains in each of which the polarization and the crystal axes may have different directions. Domains are separated by interfaces called domain walls.

A single domain can be obtained by domain wall motion made possible by the application of electric field. A very strong field could lead to the reversal of the polarization in the domain and it is known as domain switching.

When electric field is applied, then the domain for which the polarization points along the direction of the applied field grow at the expense of other domains for which the polarization points in other directions.

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FERROELECTRIC MATERIALS, HYSTERESIS CURVE AND SPONTANEOUS POLARIZATION

In ferroelectric materials, the polarization P does not vary linearly with electric field E.

Hysteresis curve: The plot of P versus E in which the material is polarized in one direction and then in opposite direction is called the hysteresis curve of the specimen.

When a piece of ferroelectric material initially unpolarized, is subjected to a gradually increasing electric field, the polarization P varies with E.

Remanent polarization or retentivity or remanence: Continue reading “FERROELECTRIC MATERIALS, HYSTERESIS CURVE AND SPONTANEOUS POLARIZATION”

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Applications of Piezoelectric effect

Last time I have discussed about the piezoelectricity. Let us discuss about the applications of piezoelectric effect.

(a) Electro-mechanical transducers.

Piezoelectric effect is used to convert electrical energy into mechanical energy and vice-versa, that is the piezoelectric substances are used as electro-mechanical transducers.

If an electric signal is applied to one end of a quartz rod, the variations in strain generated in the rod in consequence of the effect propagate down the rod, resulting in a mechanical wave, or an acoustic wave on reaching the other end of the rod.

(b) Highly stable oscillators: Continue reading “Applications of Piezoelectric effect”

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PIEZOELECTRICITY

Definition: When certain crystals become electrically polarized that is electric charges appear on their surface when stressed then this phenomenon is called the piezoelectric effect, or piezoelectricity and the crystals as the piezoelectric crystals.

Examples: Quartz, rochelle salt, tourmaline are piezoelectric substances.

The inverse effect-that these crystals become strained when polarized (i.e. place in an electric field) has also been observed.

Piezoelectric strains are very small, and the corresponding electric fields are very large.

Example. In Quartz a field of 100 V/cm produces a strain of the order of 10-7.

Origin of piezoelectric effect: Continue reading “PIEZOELECTRICITY”

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