Origin of Ferroelectric Modification: The Thermal Behavior of Dopant Ions

Abstract

Ferroelectrics were often modified by dopants for corresponding applied fields. The LiNbO 3 (LN) crystal, one of the most attractive ferroelectric functional materials, was often doped by magnesium or some rare-earth ions for corresponding application. Though many kinds of dopants for the LN crystal have been researched, the mechanism of the dopant to regulate the ferroelectricity was never reported. Herein, the origin of ferroelectric modification was investigated from the thermal distortion of the fine lattice structure. It was proved by using the state-of-the-art first-principles approach based on density functional theory that the rare-earth ions and antisite Nb Li defects are poisonous to the LN lattice structure, which generates the lattice distortion. Furthermore, the lattice distortion evolved into a lattice-plane split with the increasing temperature. On the contrary, the magnesium doped LN crystal keeps the complete LN structure even at 1275 K. Finally, the mechanism of ferroelectric modification was analyzed from the thermal behavior of dopant cations.

Chemical environment and occupation sites of hydrogen in LiMO3

“…Therefore, structural and diffusion investigations are fundamental, since impurities or dopants modify the properties of the crystals. 16,17 Hydrogen, in particular, is a natural and unavoidable impurity introduced during the growth process of LiMO 3 crystals. 18 In addition, hydrogen can be easily incorporated into the oxides by a proton exchange (PE) reaction in hot acids 9 or in a wet atmosphere under high temperatures.…”

Microstructure and domain engineering of lithium niobate crystal films for integrated photonic applications

“…Until now, LN films have generally been exfoliated from nondoped congruent LN crystals. The congruent LN crystals have a large coercive field (21 kV mm −1 ) and a low optical damage threshold because of intrinsic defects 145 . An electric field of up to 40 kV mm −1 is needed to invert the ferroelectric domain in an x-cut LN film for QPM nonlinear integrated photonics.…”