A neutron diffraction study on the deuteration effect in CsH2PO4 crystal

The deuteration rate x of partially deuterated crystals, Cs(H1-xDx)2PO4, was determined through the neutron diffraction experiment. It was found that two non-equivalent positions of hydrogen atoms take slightly different deuteration rates. The deuteration rate x1 of the shorter hydrogen bond which is closely related to the ferroelectric phase transition is smaller than the rate x2 of the longer one. The observed dependence of the phase transition temperature Tc on x1 is found to be linear in contrast to the concaved dependence predicted in the one-dimensional proton-pseudospin coupled model. The neutron diffraction experiment also revealed that the distance of the shorter hydrogen bond increased linearly with x1, whereas that of the longer one remained constant. (author)