Origin and evolution of ferroelectricity in the layered rare-earth-titanate, TiO, Lichtenberg phases
arXiv:1903.11847 · doi:10.1016/j.poly.2019.07.018
Abstract
We report a systematic first-principles study based on density functional theory (DFT) of the structural and ferroelectric properties of the TiO perovskite-related oxides with La, Ce, Pr, and Nd. We show that, in all cases, the ferroelectric distortion to the ground-state polar structure from its parent centrosymmetric phase is driven by a single polar soft mode consisting of rotations and tilts of the TiO octahedra combined with displacements of the ions. A secondary centrosymmetric distortion, which is stable in the parent structure, contributes substantially to the energy lowering of the ground state. We evaluate the trends in structure and polarization across the series as a function of and reconcile discrepancies in reported values of polarization in the literature. Our results confirm that the family of TiO materials belong to the class of proper geometric ferroelectrics.
arXiv comment15 pages, 12 figures, 7 tables
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