The poling effect turns ferroelectrics into useful piezoelectrics. However, this means they can only be used within certain well defined limits. If piezoelectrics are used outside of these limits, the alignment of dipoles can disappear, leading to the depolarisation of the ferroelectric, and removing its piezoelectric properties. This can occur in a number of ways.
1. Thermal depoling
If the material is exposed to excessive heat, such that its temperature approaches its Curie temperature, the dipole moments regain their unaligned state. At the Curie temperature, a ferroelectric becomes entirely unaligned. In order to prevent this occurring, it is necessary to use piezoelectrics well below their Curie temperature.
2. Electrical depoling
A strong electric field, when applied in the reverse direction to the already poled material, will lead to depoling.
3. Mechanical depoling
The stress placed on a piezoelectric can lead to depolarisation.