Why ferroelectric materials have high dielectric constant and dielectric loss?

The value of dielectric constant depends on the magnitude of electric polarization vector while the magnitude of dielectric loss depends on dielectric constant and loss tangenttangent both. Dielectric loss is due to lag of polarization with a. c. field and is highly frequency dependent. In ferroelectric materials, dielectric constant is high due to spontaneous polarization similar to spontaneous magnetization in ferromagnetic materials. In the certain frequency range where loss tangent has certain value, dielectric loss will also be high if dielectric constant is high as dielectric loss is the product of dielectric constant and loss tangent.

The high dielectric constant simply reflects that ferroelectrics have spontaneous polarization below the ordering temperature.A small electric field suffices to create large polarization. In a linear response regime that means the susceptibility of the material is very high. The susceptibility is directly proportional the the dielectric constant. In order to have stable remanent polarization the materials has to have coercivity. That meansthe ferroelectric hysteresis loop has a certain width. If you switch between the remament polarization state there is hysteretic loss, which is determined by the area enclosed by the hysteresis. Again in a linear response regime there is still a fingerprint of this type of loss in the form of a complex component to the dielectric function, which quantifies dissipation. Microscopically you can think about this as domain wall motion where domain walls experience pinning forces one has to overcome. 

Thanku so much

High dielectric constant of ferroelectrics is the result of the contribution of the soft resonant or relaxational modes. Lossess and permittivity are related by Kramers-Kroning relation. See: J. Grigas, Microwave Dielectric Spectroscopy of Ferroelectrics and Related Materials, Gordon & Breach Publ.

High polarize-ability of thin film materials the charge separation hence capacitance effect or the permittivity must be higher. The loss is associated to the response with relaxation constant. It is directly related to permittivity and inversely to the conductivity however, conductivity is crucial to control loss while frequency band of operation is important to determine it.