Growth of the 90/spl deg/-domains in C-plates of NaNO/sub 2/

A sodium nitrite NaNO/sub 2/ crystal is usually composed of 180/spl deg/ domains. These antiparallel ferroelectric domains are of [100] twin structure. The [121] twin structure which is well-known as the other twin is produced by the mechanical stress. Recently, it has been reported that [011] twin structure is produced by an application of a high ac electric field. The [011] twin in the matrix crystal is a rod shape region elongated to a-direction with a wedge type tip. The wall of the tip is moved by an additional application of an ac electric field and the rod grows toward the a-direction. The [011] twin is regarded as the ferroelectric 90/spl deg/-domain of NaNO/sub 2/. The growth of this new domain is reported in this paper.