Paraelectric state ferroelectric/piezoelectric

Within single crystals and ceramic crystallites, respectively, the dipole moments of neighbouring domains are either perpendicular or anti-parallel to each other. For polycrystalline materials the orientation of the crystallites and thus of the domains is randomly distributed. In the original state these materials do not exhibit a macroscopic polarization and thus no piezoelectric effect. However, the latter can be induced by applying a static electric field below the Curie temperature where the domains of uniform dipole moments arrange towards the polarization field (paraelectric polarization). The field strength applied should be between the saturation and the breakdown range. Due to this polarization the ferroelectric material becomes piezoelectric. 

Concepts like piezoelectric, pyroelectric, ferroelectric, ferrielectric, antiferroelectric, paraelectric, electrostrictive, and several more, relate to distinct phenomena and are themselves interrelated. They are bound to appear in the description of liquid crystals and liquid crystal polymers, as they do in normal polymers and crystalline solids. Presently, great confusion is created by the uncritical use of these terms. For example, in the latest edition of the Encyclopedia Britannica [4] it is stated that pyroelectric-... 

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