Neutron measurements on the hydrogen bond potential in paraelectric KDP

Diffraction effects observed in elastic incoherent scattering of thermal neutrons from a single crystal of KDP are compared to two models for the proton ground states in the paraelectric phase. The comparison, taken together with the results of recent infrared absorption measurements, indicates that the protons fluctuate between two equilibrium sites at the hydrogen bonds. The distance of these two sites, the mean square proton amplitude, the overlap integral, and an approximate value for the energy difference of the symmetric and the antimetric ground states are determined.