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Single crystals of BaTiO₃ have been grown and investigated by means of the polarization microscope, x-ray diffraction, and their dielectric and piezoelectric response. It has become possible to see the domains in the ferroelectric state and to change their number, size, and orientation. Wall displacements and the alignment of such domains, for which well-known indirect evidence exists in the case of ferromagnetics, have been observed in both polarized and unpolarized light, and the influence of temperature and electric fields on the domain structure and orientation of the polar axis have been investigated. In addition to the Curie point near 120^, there exist two polymorphic transitions near 5^ and -70^. A tentative explanation for the development of the ferroelectric state is given which brings the new ferroelectric group of the titanates into close relation to those of the tartrates and phosphates.
Baum et al. (Tue,) studied this question.