Engineering Physics

6.8 Ferroelectricity

Few dielectric substances such as barium titanate [BaTiO₃], rochelle salt, KDP (KH₂PO₄), ADP [NH₄H₂PO₄], LiNbO₃, KNbO₃, etc. called ferroelectric materials show spontaneous electric polarization (P) below Curie temperature (T < T_c) is known as ferroelectricity. This is shown in Fig. 6.11(a). Polarization of a material without any applied external electric field on it below Curie temperature is known as spontaneous polarization.

The dielectric constant of a ferroelectric material increases enormously as the temperature of the material reduces to its Curie temperature. The variation of dielectric constant with temperature is shown in Fig. 6.11(b) and is given by Curie-Weiss law where C is the Curie constant and T_c is Curie ...