The Role of Proton–Proton Interaction in NH₄H₂PO₄-Type Crystals

抄録

The interaction between the protons on the nearby hydrogen bonds in NH₄H₂PO₄ (ADP)-type crystals, called the Ishibashi interaction, was analyzed to derive theoretically, i.e., not in an ad hoc way, the effective dipole–dipole interaction between PO₄ radicals, which plays a substantial role in phase transitions. It turns out that at low temperatures the ADP-type antiferroelectric phase is stabilized if the Ishibashi interaction is repulsive, while the monoclinic ferroelectric phase is stabilized otherwise.