The field-induced ferroelectric phase of sodium niobate

Antiferroelectric sodium niobate (a=5.57, b = 15.54, c=5.51 A) can be changed into ferroelectric sodium niobate (a =5.57, b = 7.77, c =5.51 /~) by the application of an electric field perpendicular to the b axis. The 'transition field' is about 50 kV. per cm. When the field is removed, the fieldinduced structure may then coexist in a single crystal with the unaltered part, not subjected to the field. With crystals of a particular orientation, changes in orientation of the field-induced area can be observed both by X-ray diffraction techniques and with the polarizing microscope.