engleski

Phase transition mechanism in hydrogen-bonded ferroelectrics

A ferroelectric phase transition is a structural phase transition in which a crystal undergoes a structural change at the critical temperature, Tc, from a high-temperature centrosymmetric phase to a low-temperature non-centrosymmetric phase that exhibits spontaneous electric polarization switchable by external electric field. Ferroelectric materials have many applications in electronics, optics, computer memory technology, etc. KH2PO4, or KDP, as a representative of hydrogen-bonded ferroelectrics, has attracted scientific interest for a long time because its phase transition shows several quantum effects and has unclear mechanism. A simple and generally accepted theoretical explanation of KDP crystal behavior is that the protons move in a double-well potential of hydrogen bonds connecting neighboring PO4 groups, while the dipoles induced by deformation and movement of PO4 groups produce electric polarization of the crystal. Spontaneous polarization below Tc appears together with the localization of protons in one of the potential wells, indicating that the dipoles of PO4 groups are strongly coupled to the protons. In traditional models, the localization and ordering of the protons within hydrogen bonds is a dominant mechanism of the phase transition, while ordering of PO4 dipoles and spontaneous polarization are only the net effects. However, recent experimental data and models suggest the opposite.

Phase transition; Hydrogen-bonded ferroelectrics

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