1/1/14 Piezoelectric Materials - Poling

www.chm.bris.ac.uk/webprojects2004/phillips/PZ/pz-poling.html 1/1

Potentially piezoelectric materials can be forced to be piezoelectric by a process called

poling. This process can only be carried out at temperatures below the Curie point,

when the crystal st ructures cause an electric dipole to be created. In perovskite

structures the dipole is created by movement of the central ion in the structure (usually

a large metal ion). Above the Curie point the central ion is on average in the plane of

the structural ions, but below the Curie temperature the central ion moves out of the

plane of the structural ions and so the charges no longer balance and give a dipole.

Perovskite structure: a) Above Curie point b) Below Curie point

The process of poling involves aligning all of these individual dipole moments, so that

they all point in the same general direct ion. This is accomplished by putt ing the crystal

in a constant electric field to force the dipoles to align. In the electric field each dipole

will feel a torque if it is not parallel to the field lines produced, and so is turned to that

direct ion. When the electric field is removed, the dipoles remain fairly aligned, although

there will st ill be some element of random direct ion.

Click on this sect ion of a piezoelectric material to see the effect of an

electric field applied vert ically upwards on the dipoles within it .