Electric-field-induced structural changes in KH2PO4 at room temperature and at 167 K - art. no. 134105

In this paper we report on the electric-field-induced changes in the struct ure of KH2PO4 (KDP) at two different temperatures determined by x-ray diffr action. One data set was measured at room temperature and the other at 167 K, significantly closer to the phase transition temperature of 122 K. The i nduced structural changes were determined from the measured changes in the integrated x-ray-diffraction intensities by means of a least-squares refine ment. As expected, the structural changes induced at room temperature are e nhanced when approaching T-C. The structural changes include the shifts of the atoms and the ordering of the hydrogen. At 167 K and in the presence of all electric field of 4 x 10(6) V/m parallel to the c axis. the P atom is displaced by 29(2) x 10(-4) Angstrom along the c axis, and a redistribution of the hydrogen over the two formerly equivalent sites in the hydrogen bon d takes place. The site towards which the P atom moves is decreased in occu pancy in favor of the other by an amount of 1.4(5)%. The distortion of the oxygen framework is marginal. The induced structural changes in KDP are com pared to those induced in its deuterated isomorph KD2PO4 (DKDP), which we m easured previously [van Reeuwijk et al., Phys. Rev. B 62, 6192 (2000)]. The features of the structural changes induced in KDP and in DKDP are very sim ilar. The ratio of the two main structural changes, i.e., the ordering of t he proton in the hydrogen bond to the shift of the phosphor atom, is, howev er, isotope specific. Our results show great similarities with the observed structural changes around T-C.