Editing Dielectric (section)

==Paraelectricity==
{{See also|Ferroelectricity}}

Paraelectricity is the nominal behaviour of dielectrics when the dielectric permittivity tensor is proportional to the unit matrix, i.e., an applied [[electric field]] causes polarisation and/or alignment of dipoles only parallel to the applied electric field. Contrary to the analogy with a paramagnetic material, no permanent [[electric dipole]] needs to exist in a paraelectric material. Removal of the fields results in the dipolar polarisation returning to zero.<ref>{{cite book|last=Chiang|first=Y.|year=1997|title=Physical Ceramics|publisher=[[John Wiley & Sons]]|location=New York}}</ref> The mechanisms that causes '''paraelectric''' behaviour are distortion of individual [[ions]] (displacement of the electron cloud from the nucleus) and polarisation of molecules or combinations of ions or defects.

Paraelectricity can occur in [[crystal]] phases where electric dipoles are unaligned and thus have the potential to align in an external [[electric field]] and weaken it.

Most dielectric materials are paraelectrics. A specific example of a paraelectric material of high dielectric constant is [[strontium titanate]].

The [[lithium niobate|LiNbO<SUB>3</SUB>]] crystal is [[ferroelectric]] below 1430 [[Kelvin|K]], and above this temperature it transforms into a disordered paraelectric phase. Similarly, other [[perovskite]]s also exhibit paraelectricity at high temperatures.

Paraelectricity has been explored as a possible refrigeration mechanism; polarising a paraelectric by applying an electric field under [[adiabatic|adiabatic process]] conditions raises the temperature, while removing the field lowers the temperature.<ref>{{cite journal|last1=Kuhn|first1=U.|last2=Lüty|first2=F.|doi=10.1016/0038-1098(65)90060-8|title=Paraelectric heating and cooling with OH—dipoles in alkali halides|journal=Solid State Communications|volume=3|issue=2|page=31|year=1965|bibcode=1965SSCom...3...31K}}</ref> A [[heat pump]] that operates by polarising the paraelectric, allowing it to return to ambient temperature (by dissipating the extra heat), bringing it into contact with the object to be cooled, and finally depolarising it, would result in refrigeration.