Ferro electric behavior of solids, Physics

Assignment Help:

In physics, the dielectric material such as Rochelle salt and barium Titan ate with a domain structure containing dipoles (a symmetric distributions of electrical charge) which spontaneously align. If the centre of the gravity of the positive and negative charges in a body does not coincide in the absence of an applied electric field, the substance is called Ferro Electric.

 

Ferroelectric crystals often show several curie points and domain structure hysteresis much as do ferromagnetic crystal. When the temperature exceeds a certain value called the curie point, the substance losses its Ferro electric properties. Above the curie point the formation of small regions-domains-is disrupted by thermal agitation and the permittivity is reduced to the usual small value. Below the Curie point, the whole crystal becomes spontaneously polarized. Examples of Ferro electric materials are Rochelle salt, Potassium dihydrogen phosphate and its isomorphous salts and Barium Titanate.The Curie point for Rochelle salt is about 24degreeC and this substance has a very narrow temperature range of about 40degreeC within which it is ferroelectric.

The Curie point for Barium Titanate is 130degreeC above approximately 130degreeC the crystal structure of Barium Titanate has cubic unit cell. The centre of the mass of the negative charges and the positive charges, Ba2+ and Ti4+ ion. There is therefore no net polarization and p=0. Above 130degreeC, therefore, the barium titanate crystal exhibits no permanent polarization and is not ferroelectric. However, below 130degreeC, the structure of barium titanate is tetragonal in which the Ti4+ atom is not located at the centre of mass of the negative and positive charges. The crystal posses a finite polarization vector P and is ferroelectric.

An important and technologically useful characteristic of a ferroelectric crystal is its ability to be poled. Above 130degreeC there is no permanent polarization in the crystal. If we apply a temporary field E and let the crystal cool to below 130degreeC, we can induce the spontaneous polarization P to develop along the field direction. In other words, we would define the c axis is the polar axis along which P develops. It is also called the ferroelectric axis. Ferroelectrics often have very large dielectric constants, and thus are often used as the dielectric material in capacitors. They also often have unusually large nonlinear optical coefficients.

There are two main types of ferroelectrics: displacive and order-disorder. The effect in barium titanate, a typical ferroelectric of the 'Displacive Type' is due to a polarization catastrophe, in which, if an ion displaced from equilibrium slightly, the force from the local electric fields due to the ions in the crystal increase faster than the elastic restoring forces. This leads to a symmetrical shift in the equilibrium ion positions and hence to a permanent dipole moment. In an order-disorder ferroelectric, there is a dipole moment in each unit cell, but at high temperatures they are pointing in random directions. On lowering the temperature and moving through the phase transition, the dipoles order, all pointing in the similar direction in a domain.


Related Discussions:- Ferro electric behavior of solids

Properties of lines of flux, Properties of Lines of Flux To make the im...

Properties of Lines of Flux To make the imaginary lines of flux describe the behaviour of the magnetic field we must give them appropriate properties.  Thus lines of flux have

Force, What is resultant force

What is resultant force

Schwarzschild radius, Schwarzschild radius The radius r of the event h...

Schwarzschild radius The radius r of the event horizon for Schwarzschild black hole of mass m is provided through (in geometrized units) r = 2 m. In conventional units, r =

Angular speed, A ballerina begins a tour jete with angular speed ?i and a r...

A ballerina begins a tour jete with angular speed ?i and a rotational inertia consisting of two parts: Ileg = 1.55 kg*m^2 for her leg extended outward at angle ? = 90.0 to her body

What effect does this have on eclipses, Q. If the moons orbit is inclined s...

Q. If the moons orbit is inclined somewhat relative to the Earth's orbit what effect does this have on eclipses? Answer:- This makes eclipses rarer as well as if the moon's

Pulses, what exactly is pulse height analysis

what exactly is pulse height analysis

What is Solid State Physics?, Can you please explain what is solid state ph...

Can you please explain what is solid state physics? I need some help from you guys for my short report about it :) Thanks!

Tardon, Tardon A particle that has a positive real mass & travels at a ...

Tardon A particle that has a positive real mass & travels at a speed less than c within all inertial frames.

Static limit, Static limit: The distance through a rotating black hole...

Static limit: The distance through a rotating black hole where no observer can probably remain at rest (w.r.t. the distant stars) due to inertial frame dragging; this region i

What is meant by the sensitivity of a potentiometer, What is meant by the s...

What is meant by the sensitivity of a potentiometer? A battery E 1 of 4 V and a variable resistance R h are linked in series with the wire AB of the potentiometer. The length

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd