Self-Consistent Nonlinearly Polarizable Shell-Model Dynamics for Ferroelectric Materials

Abstract

We investigate the dynamical properties of the polarizable shell-model with a symmetric double Morse-type electron-ion interaction in one ionic species. A variational calculation based on the Self-Consistent Einstein Model (SCEM) shows that a theoretical ferroelectric (FE) transition temperature can be derived which demonstrates the presence of a first-order phase transition for the potassium selenate (K 2 SeO 4 ) crystal around Tc = 91.5 K. Comparison of the model calculation with the experimental critical temperature yields satisfactory agreement.

Effects of Quantum Fluctuations and Deformability Parameter on Structural Phase Transitions for Ferroelectric Materials with Deformable Double-Well Potentials

“…which follows from the self-consistency equations ( 33) and (34) for T = 0. From the same equations, one finds for = c ,…”

“…Examples are the displacements of the Ti ions with respect to the O 6 octahedra in BaTiO 3 , the rotations of the O 6 octahedra in SrTiO 3 , the rearrangement of the protons in the double-well potentials of the O H• • •O hydrogen bonds in hydrogen bonded ferroelectrics. In those systems, the shape of the nonlinear single-site potential may deviate considerably from that attributed to the local potential, as in the hydrogen-bonded systems, where the large displacement of the heavy ions can significantly modify the barrier height of the double-well potential associated with the light protons [34]. Otherwise, the basic idea of the model proposed by Antonchenko, Davydov, and Zolotariuk [35] is that the coupling between heavy ions (oxygen atoms) can provide a mechanism which changes the potential barrier that protons have to overcome to jump from one molecule to another and make their motion easier.…”

“…Otherwise, the basic idea of the model proposed by Antonchenko, Davydov, and Zolotariuk [35] is that the coupling between heavy ions (oxygen atoms) can provide a mechanism which changes the potential barrier that protons have to overcome to jump from one molecule to another and make their motion easier. Also, in the hydrogenbonded systems and particularly in ferroelectrics such as KH 2 PO 4 or KD 2 PO 4 (KDP-type crystals), it is now well recognized that the variation of distance between the heavy ions that surround a proton modulates the double-well experienced by the protons [34,36].…”