The molecular aspect of ferroelectricity in KDP crystals

Abstract

Abstract The totality of structural and spectroscopic data implies that the H2PO4 − groups in the crystal lattice of the ferroelectric phase of KDP represent molecular formations. Their structure, force field and charge distribution are determined by the covalent binding pattern. Spontaneous polarization in the ion-molecular model of a crystal is represented by a sum of the oppositely directed surface contribution and bulk polarization. The bulk polarization is produced by the molecular dipoles of the anions, and the surface contribution, by charged surface layers created at the polar faces by proton ordering. The surface contribution being predominant, the spontaneous polarization of a crystal is directed opposite to the anion dipole moments. A detailed analysis of the charge distribution in molecular anions reveals that the polarization is primarily due to the electronic populations of the O and OH atoms in the structure being nonequivalent.