Ferroelectricity is temperature dependent phenomena

Ferroelectricity is temperature dependent phenomena. Spontaneous polarization exists below a temperature defined as Curie temperature TC. Above TC, ferroelectric materials undertake a phase transition to normal dielectrics that are paraelectric. The variation of Pr as a function of temperature in ferroelectric materials is schematically shown in Figure 2.4 a. Moreover, upon heating, the dielectric permittivity of the ferroelectric phase presents an irregular variation; that is it increases abruptly around the Curie temperature to decrease again at temperatures above the transition point. The decrease of the dielectric permittivity above the Curie temperature is conventionally described by the Curie-Weiss’ law:
?_r/?_0 =C/(T-T_C )
Figure 2.4 b schematically depicts the temperature dependence of the dielectric constant around the Curie temperature.