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Kinetics of Domain Nucleation in Ferroelectric Ba5Ti2O7Cl4

Kinetics of domain nucleation in the ferroelectric Ba 5 Ti 2 O 7 Cl 4 has been studied. It is shown that the domain nucleation in this crystal is helped substantially by point defects that are ordered in the structure on account of appreciable strain energy associated with them. When the crystal is subjected to electrical or mechanical stress, these point defects get perfectly ordered and nucleate domains around them. This can be noted when the crystal surfaces are observed under reflected light in a metallurgical microscope. The defects become observable as etch pits developed at their sites, and the nucleated domains have domain lines that appear as dark lines in the microscope. Interestingly, this situation is exactly similar to the one found by Ingle and coworkers in KNbO 3 . Hence, for studying the kinetics of nucleation the model of nucleation given by Ingle and coworkers has been used. The spontaneous polarization, surface energy of the domain walls, activation energy for the nucleation of the microdomain, and also the width of the domain wall have been calculated. It is shown that the process of domain nucleation is equivalent to the nucleation of a pair of domain walls. Thus, nucleation of a domain wall shall been shown as a physical process distinct from the nucleation of a domain.