Among the ferroelectric materials, the static dielectric constant depends on the temperature under the relation: Curie – Weiss relation: €r = P + Q/ (T-Tc), (T> Tc), P, Q are constants temperature independent. C = Curie constant Tc = Curie temperature
A transition in phase is observed at temperature Tc. Above this, the material remains in Paraelectric phase (the phase where the elementary dipoles of different crystal unit cells are randomly oriented). Below this, the material is present in ferroelectric phase. Figure 4: The ferroelectric hysteresis loop 
Ferroelectric materials are investigated based on their behavior when an external electric field …show more content…
The advantage of bulk materials is they act as insulators and on the other hand, thin films are semiconductors. External environment and strain with in the film play a major role in the use of thin films. The effects caused by sizing depends on the boundary conditions that act as limit to ferroelectric phase. The effects of sizing can be formation of Schottky between the ferroelectric and the electrode, ionic mobility defects, domain and switching.
Strain occurs because of the mismatch in the lattice structure involving the film and the substrate. The strain shows that mechanical boundary conditions also distorts the ferroelectric properties of material. The defects caused by strain are not negligible. To maintain the required strain, it is suggested that the film size is doubled, temperature and polarization are maintained accordingly.
In brief Ferroelectric materials: Principles
• Ferroelectric materials usually have two stable polarization states that are switchable based on the applied electric field. The remnant polarization Pr coercive field strength Ec are the parameters that describe the functionality of a ferroelectric material and the hysteretic behavior associated with