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Depolarisation methods
P T
Thermal depoling

Near the Curie point, the net polarisation disappears, as the dipole moments unalign.
Electrical depoling
When an alternating electric field is placed over a piezoelectric to generate ultrasound, the reversed field depolarises the piezoelectric, given a strong enough field.

Mechanical depoling
A small stress, when applied to the piezoelectric, causes it to develop a charge, as seen previously. However, if the stress applied is too great, the atomic positions are completely changed, the dipole moments unalign, and the polarisation disappears.