Understanding how different structural phases interact differently (and/or similarly) with finite electric displacement D fields is of fundamental importance in determining the phase stability and field-induced properties, but little knowledge is known. Using a combination of analytic formulation and first-principles calculations, we investigate how different structural phases in ferroelectric Lithium Niobate (${\mathrm{LiNbO}}_3$) interact with finite D fields. Three important (low-energy) structural phases are considered, which include the polar TO phase caused by soft transverse-optic (TO) phonon, the LO phase caused by soft longitudinal-optic (LO) phonon, and the nonpolar (nonP) phase. Our results reveal several key outcomes: (i) Different structural phases display interesting (and notably different) free-energy landscapes when they interact with finite D fields. While the LO phase exhibits dual free-energy minima at low D fields, the TO phase shows only a single free-energy minimum. (ii) The LO and TO phases show drastically different field-induced tunability of polarization. The polarization of the TO phase alters dramatically with the D field. In contrast, the polarization of the LO phase shows an unusual resistance to the D field. (iii) A pronounced phase transition is discovered in ${\mathrm{LiNbO}}_3$ under finite D fields (in which the solid transforms from a nonpolar phase to the polar TO phase), and the critical D field is determined to be 0.07 ${\mathrm{C}/\mathrm{m}}^2$. The phase transition is found to be second order, and the free-energy barrier of phase transformation is shown to depend on the D field significantly. The physical origin underlying the profound differences in the field-induced responses between the LO and TO phases is provided, and is revealed to be dictated by the mode effective charge.

Close

PrevNext

View figure in article

• Electric polarization
• Ferroelectricity
• Phase transitions
• Ferroelectrics
• First-principles calculations