Electric-field-induced structural changes in deuterated potassium dihydrogen phosphate

In this paper the electric-field induced distortions in the unit cell of bo th KDP (KH2PO4) and DKDP (KD,PO,) as function of temperature ard measured u sing x-ray diffraction. For both compounds the d(36) shows a Curie-Weiss be havior, with constants 3.61(3)x10(-9) KC/N for KDP and 4.4(2)x10(-9) KC/N f or DKDP. For DKDP we measured the electric-field induced change in integrat ed intensity of a number of reflections at room temperature. These changes were submitted to a refinement where the shifts of the atoms and the orderi ng of the deuteriums were determined. In the presence of an electric field of 2.7x10(6) V/m parallel to the c axis, the P atom is displaced by 27(3)x1 0(-4) Angstrom along the c axis, and a redistribution of the deuteron over the two formerly equivalent sites takes place. The site towards which the P atom moves is decreased in occupancy in favor of the other by an amount of 0.8(2)%. The distortion of the oxygen framework is marginal. These results agree very well with experiments where the phase transition was induced by cooling below T-C. On the basis of the structural changes, the calculated electric-field induced polarization was 0.18(4) mu C/cm(2) consistent with other experiments. Based on our findings we discuss the sequence of the mai n structural changes involved in the phase transition.