A Neutron Diffraction Study of the Ferroelectric Transition of CsH₂PO₄

LATTICE DYNAMICS OF A MONOCLINIC CsH_{2}PO_{4} CRYSTAL

“…As follows from this figure, the Cs + and (PO 4 ) − ions shift along the b axis in opposite directions with simultaneous PO 4 group rotation in the ac-plane. The calculated displacements of structural units both translational and rotational are in good qualitative agreement, with neutron scattering data [12]. In figure 7a, the dispersion relation of the soft phonon mode A u in the plane (b 1 , b 3 ) at T = 130 K and P = 241 MPa is depicted.…”

“…The protons on the longer bonds are ordered on one of the two possible equilibrium sites at all temperatures. At T c = 156 K and atmospheric pressure, a CDP crystal undergoes the PT into the PE phase with the space group P 2 1 and the spontaneous polarization P s b (Z = 2, a = 7.87Å, b = 6.32Å, c = 4.89Å, β = 108.3 o at T = 83 K [12]). In the PE phase a proton ordering on the shorter hydrogen bonds occurs.…”

“…Owing to their interesting properties, the CDP crystal and its deuterated analogue CsD 2 PO 4 (DCDP) have been intensively studied by X-ray diffraction [11,21,34], neutron scattering [9,12,22,33], dielectric [5,7,31] acoustic [1,14,24], Raman scattering [8,13,20,38], hyper-Raman scattering [28], IR absorption [30] and optic [35] measurements. However, a lattice dynamics of the CDP crystal in the region of phase transitions (PTs) and a triple point have been investigated insufficiently.…”

Thermodynamics and dynamical properties of the KH_{2}PO_{4} type ferroelectric compounds. A unified model

“…In the first case, the phase transition becomes antiferroelectric; in the second case the crystal symmetry and structure of the hydrogen bond system change. In the CsH 2 PO 4 type ferroelectrics, the proton ordering on hydrogen bonds is quasi-one-dimensional (see [34][35][36][37][38][39][40]). The same holds for PbHPO 4 ferroelectrics (see [41][42][43][44]).…”

On the vibrational properties of CsD2PO4 crystal

“…Nevertheless, the underlying phase-transition mechanism remains controversial. By analogy with KDP crystals many authors [1][2][3]15] treated the proton ordering below the phase-transition point in DCDP as a trigger for the subsequent displacement of the heavy PO 4 groups. On the other hand, X-ray analysis data corroborate an assumption about the reversal motion of PO 4 tetrahedra between two possible positions around the mirror plane in the paraelectric phase [3,4] with the following arrangement of PO 4 groups in one of two possible sites below the phase-transition point.…”