Abstract
The thermal depolarization of crystals of NH 4Cl polarized above the phase transition temperature (242.5K) by an applied electric field was studied in 13 crystals prepared under a variety of conditions in order to examine the effects of doping with divalent anions or cations and of acid or alkaline conditions during crystal growth. All the features found in crystals grown from solution also occur in a crystal grown from the vapor. We may conclude, therefore, that the depolarization effects observed are properties of crystalline NH 4Cl and are not due to water or urea occluded during crystal growth. Four main depolarizations were observed: one of these is ascribed to space charge and the other three are attributed to dipole relaxation processes. The activation energies for these are 0.58, 0.73, and 0.85 eV, respectively. The various doping experiments lead to the conclusion that one of these is favored by acid conditions and the presence of cation vacancies and the other two by alkaline conditions and the presence of anion vacancies. Specific models for the dipolar defects are formulated and discussed.
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