Ferroelectric materials versus Piezoelectric materials

[nabs16]

Hello every one.

Ferroelectric materials have spantaneous polarization but i read in many articles that these ceramics are polarized by applying an electric field. Why polarize ceramics that are already polarized ?

Thanks.

 

[Charles Link]

I can only guess a little at this one, but before application of the electric field, it is possible the polarization is somewhat random with near zero net polarization. For ferroelectric materials of the permanent magnet type, I believe they apply a somewhat weak to moderately strong external magnetic field as the magnet cools from the molten state and above the Curie temperature to below the Curie temperature, so that the permanent magnetization is ordered and in one direction, as opposed to being somewhat random throughout the material, as might occur with cooling without application of an external magnetic field.

 

[nabs16]

It makes sense. Thanks for the explanation but If the polarization of ferroelectric materials is near to zero before applying an electric field, what is the difference between a classical piezoelectric material (such as quartz) and a ferroelectric material ?

 

[Charles Link]

A piezoelectric material develops a strain (a length change) upon application of the electric field. $\\$ I believe some ferroelectric materials have a spontaneous polarization in the absence of an applied field. In addition, I believe in many cases they also respond very strongly to the applied field with a very large $\chi$, where $P=\chi E$. Materials that would be considered ordinary dielectrics have a smaller value of $\chi$.

 

[Lord Jestocost]

There is a freely available chapter from the book “Dynamic Fracture of Piezoelectric Materials” (http://www.springer.com/de/book/9783319039602) which deals with the topic “Piezoelectric Materials” and the “poling” of ferroelectric materials ([PDF]Piezoelectric Materials - Springer).

 

[nabs16]

Thanks guys ;)

 

[Baluncore]

Ferroelectric materials have spantaneous polarization but i read in many articles that these ceramics are polarized by applying an electric field. Why polarize ceramics that are already polarized ?

Neutral ceramics can be polarised by physical stress. If a permanent polarisation is required then an electric field is applied during manufacture. The key term that is missing is " electret ".