Imprint in ferroelectrics is defined as the shift of the hysteresis characteristics along the voltage axis and the loss of the remanent polarization state opposite to the built one (see Figure 1792). The imprint effect indicates the preference of one polarization state over the other or the lack of ability to distinguish between the two different polarization states +P_r and -P_r (see page3544).

A couple of mechanisms were proposed to interpret imprint effects in ferroelectrics:
         i) An internal bias in the ferroelectric layer is built due to defect dipole alignment, resulting in a shift of the hysteresis loop [1]. This dipole alignment originates from acceptor ions and oxygen vacancies.
         ii) A thin surface layer suppresses the ferroelectric properties. [2]
         
         

[1] G. Arlt, H. Neumann: Ferroelectr. 87, 109 (1988).
[2] M. Grossmann: Dissertation, RWTH Aachen (2001).