Order-disorder character of the hydrogen bond in KH2PO4

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Abstract
A discussion is presented on some of the available evidence for the shape of the local effective potential for the hydrogen motion in KDP-type ferroelectrics, particularly regarding the existence or nonexistence of a central barrier in that potential. For this purpose a one-minimum square-well potential model is considered and compared with the corresponding tunneling model. The comparison of results so obtained for both models with available experimental data on the isotope dependence of the critical temperature, Curie constant, and maximum spontaneous polarization at absolute zero leads to the conclusion that the accuracy of the experimental data together with the uncertainties on the theoretical calculations do not yet permit a discrimination in favor of an order-disorder double-well character for these ferroelectric crystals.