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The nucleation and growth of ferroelectric domains in barium titanate have been studied as a function of applied electric field and temperature. The optical and electrical measurements were made on thin single-crystal plates normal to $c$, the polar direction. When the electric field applied along this direction is reversed, new domains with opposite polarization are formed. The manner of growth of these domains is very different from that of domain growth in ferromagnetic materials. The sidewise motion of the 180\ifmmode^\circ\else\textdegree\fi{} side walls (walls between domains with antiparallel polarization) which is common in ferromagnetic crystals is almost never found in barium titanate. Instead its polarization is changed by the formation of very many new anti-parallel domains which are extremely thin (${10}^{\ensuremath{-}4}$ cm) and appear to grow only in the forward direction. The explanation of this behavior is found in the weak coupling between the dipoles perpendicular to the dipole direction. The wall thickness is small, of the order of one to a few lattice constants; the wall energy in BaTi${\mathrm{O}}_{3}$ is of the order of 10 erg/${\mathrm{cm}}^{2}$. Electrical pulsing experiments substantiate the optical observations very clearly. Pulsing the samples at different temperatures shows that the nucleation rate of new domains is accelerated at elevated temperatures. Furthermore, the growth of the new domains is faster at higher temperatures. Experimental results are presented showing how the switching current and the switching time depend on applied electrical field, on temperature, and on the size of the sample.

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.

The dielectric constants, the spontaneous polarization, and the optical properties of BaTi${\mathrm{O}}_{3}$ single-domain crystals have been measured as a function of temperature. It is shown that the deformation of the crystal in the tetragonal state is proportional to the square of the spontaneous polarization, in analogy to the behavior of the other ferroelectrics, and that the temperature dependence of the birefringence is proportional to the square of the spontaneous polarization. The change of the polarization at the two lower transition points is consistent with the assumption that the Ti ions in the oxygen octahedra are displaced from the [001] to the [011] and later to the [111] direction.

The electromechanical response of BaTi${\mathrm{O}}_{3}$ single-domain crystals was investigated as a function of temperature from room temperature to above the Curie point. It was found that when we eliminate domain effects, either by using a perfect single-domain crystal or by aligning the domains by an external electric field, we are dealing with a true linear piezoeffect. The linear piezoeffect was measured by both a static and a dynamic method. The values of the ${d}_{31}$ piezoelectric coefficient were compared with those calculated from the dielectric constant and the spontaneous polarization. The behavior of the piezoelectric resonance frequency was observed also through the same temperature range. Although the crystal is cubic above the Curie point and has a center of symmetry, the piezoelectric response persisted under the application of an external d.c. field because the external field will induce a tetragonal crystal structure through the electrostrictive effect, so that the crystal becomes piezoelectric again above the Curie point. Optical and dielectric measurements were found to verify these results.

Guanidine aluminum sulfate hexahydrate is ferroelectric over a large range of temperatures including room temperature. It is the parent of a family of materials in which the aluminum cation and the sulfate anion can be replaced by the anions and trivalent cations which form alums, for example Ga3+, Cr3+, and SeO 4 −. Replacement of guanidine has so far proved impossible, The material is trigonal, with perfect cleavage in the basal plane; the trigonal axis is the ferroelectric direction. The space group is C 3v (2) — P3lm, and the unit cell contains three molecules. It can be readily grown from water solution by standard techniques.