A neutron-diffraction study of the ferroelectric transition of potassium dihydrogen phosphate

Abstract
Neutron-diffraction measurements demonstrate that the hydrogen atoms in the ferroelectric form of potassium dihydrogen phosphate are in ordered positions, in accordance with Slater’s theory and the polar orthorhombic structure. The maintenance of a crystal as a single ferroelectric domain by application of an electric field along theZ-axis is illustrated, and the diffraction spectra show that reversal of the field direction produces a shift of the hydrogen atoms along the O—H—O bonds from one set of ordered positions to the other. A detailed study is made of the thermal motion of the hydrogen atoms at 77, 132 and 293° K, and it is found that the motion within the potential well defined by the KPO framework is practically independent of temperature and is due to zero-point energy. Parameters are determined for all the atoms at each temperature and discussed with reference to other published data.