FERROELECTRIC DISPLACEMENT OF ATOMS IN ROCHELLE SALT

The crystal structure of Rochelle salt in the ferroelectric phase is s tudied by means of x-ray diffraction. The structures of the two parael ectric phases are also redetermined to obtain the displacements of the atoms owing to the phase transitions. Cooperative displacements of th e atoms responsible for the appearance of the spontaneous polarization are obtained. The displacements consist of the movements of the tartr ate molecules,and the water molecules in a frame composed of K and Na ions. During the successive phase transitions there are several intera tomic distances maintained constant. The direction of planes made of c arbons of the tartrate molecules is practically unchanged throughout t he phase transitions.