Nucleation Of New Domains Research Articles

Electro-Optic Kerr Effect and Polarization Reversal in Deuterium-Doped Rochelle Salt

Polarization reversal as a function of nucleation and growth of domains in ferroelectric deuterium-doped Rochelle salt was investigated by means of the electro-optic Kerr effect. The results indicate that a phenomenological model based on statistical nucleation of domains in a plane including the ferroelectric axis followed by a two-dimensional sidewise expansion of the domains, will adequately account for the experimental observations for fields larger than 50 volts/cm. For lower fields, the process is controlled primarily by the nucleation of new domains due to localized stresses which hinder the displacement of domain walls.

Switching Mechanism in Triglycine Sulfate and Other Ferroelectrics

The reversal of the spontaneous polarization in a ferroelectric crystal is governed by two mechanisms: the nucleation of new domains and the growth of these domains by domain wall motion. We have investigated the switching properties of triglycine sulfate (TGS) as a function of applied electric field, temperature, and thickness of the samples.It is proposed that at low fields nucleation is the slower mechanism and hence dominates the switching process while at high fields domain wall motion determines the rate of switching. The former process leads to an exponential dependence of switching time on applied electric field and the latter to a linear dependence.A model for the nucleation and domain wall motion is treated mathematically and is compared with experimental observations. The shape of the switching current pulse was found to yield much information. The shape depends strongly on the applied electric field and is correlated with the nucleation time as well as the domain wall motion time. The asymmetry of the pulse increases with decreasing field and can be associated with the interaction between domains and domain nuclei. This interaction in various ferroelectrics is discussed and its relation to the switching is considered.

Effect of Space Charge Fields on Polarization Reversal and the Generation of Barkhausen Pulses in Barium Titanate

The rate of generation of Barkhausen pulses in barium titanate when the polarization direction is slowly reversed is profoundly influenced by the form of the voltage cycling given to the crystal. It is concluded that the rate of nucleation of new domains is determined by the field near the electrodes which, in turn, is the resultant of the applied field and a relaxing space charge field. This result follows directly if the Barkhausen pulses represent individual nucleations though this assumption is not crucial since the generation rate of the pulses parallels the total current at all stages of the polarization reversal. It is concluded also that the majority of the Barkhausen pulses occur independently of each other and of their surroundings.

Switching Time in Ferroelectric BaTiO3 and Its Dependence on Crystal Thickness

The switching time ts and the switching current imax have been measured as a function of applied field E and of the size of the sample. It has been observed that the ``activation field'' α for the nucleation of new domains is inversely proportional to the thickness of the sample. This behavior can be explained by assuming a surface layer. The thickness of this layer has been calculated to be of the order of 10−4 cm. The same way we can explain the thickness dependence of the 60-cycle coercive field strength. Furthermore, it has been found that the switching time depends to a first approximation linearly on the thickness of the sample if the field E is kept constant. This can be explained by assuming a domain wall motion primarily in the forward direction or by assuming a nucleation mechanism. The maximum velocity of the domain growth was found to be of the order of the velocity of sound. The switching time does not depend on electrode area.