A capacitor consists of a dielectric material sandwiched between two electrodes. Its capacitance can be given by,
ε0 -- The permittivity of free space
εr -- The relative dielectric permittivity of the dielectric material
A -- The area of electrodes
t -- The distance between the electrodes
A large dielectric constant, a large area and a small thickness can provide a high volumetric efficiency (capacitance per unit volume).
Ferroelectrics are important materials providing outstanding dielectric, piezoelectric, and ferroelectric properties and are widely used in the field of capacitors, transducers, actuators, filters, sensors, and random access memories.
It can be of interest as capacitors if a material exhibits high permittivity at the room temperature. The origin of high permittivity of some materials can be the extrinsic effect associated with electrical heterogeneities, e.g. the insulating grain boundaries between semi-conducting grains of CaCu3Ti4O12.