STRUCTURAL-CHANGE IN THE PARAELECTRIC PHASE OF ROCHELLE SALT

Temperature dependence of crystal structure of Rochelle salt in the lo wer paraelectric phase is studied by X-ray diffraction. Especially the circumstances of the cations and behaviours of tartrate and water mol ecules are presented. The shape and the orientation of tartrate molecu le do not show temperature dependence in the lattice of potassium ions . The tartrate molecules are tightly connected along the b-axis throug h O(8) water molecule each other and they tightly conncted to potassiu m atoms so that the tartrate molecules, O(8) water molecule and potass ium atoms make a tight sheet parallel to the b-c plane. Also O(8) wate r molecules contact to potassium atoms along the a-axis and the intera tomic distances depends on temperature. The interatomic distance betwe en O(9) and O(10) water molecules does not depend on temperature, howe ver the pair of the water molecules rotate with temperature.