抄録
A new type of twin structure is found in sodium nitrite crystals. The twin structure was studied by optical, etching, electronmicroscopic, interferometric and x-ray methods. It is established by x-ray study that this twin structure is reflection or rotation twin with {121} as twin plane. Etching experiment indicates that the head-to-tail configuration of spontaneous polarization vector is realized, and suggests that the rotation twin is the case.
This twin structure is produced by mechanical stresses, and some terrace formation is observed on the cleaved face by an interference microscope after producing the twin lamellae.
Electronmicroscopic observation shows that the twin lamellae are ca. 1μ∼5μ thick.
High electric field applied for a long period caused no twin boundary movement, though antiparallel domain walls move under the same condition. The twin structure disappears gradually on increasing temperature, and the disappearance does not take place sharply at the ferroelectric Curie point.
It is also concluded that the twin has no special interaction with ferroelectricity, except that a strong head-to-tail dipole coupling of ferroelectric crystal affects the antiparallel domain structure.
