Noncentrosymmetric structural transitions in ultrashort ferroelectric AGaO${}_3$/A'GaO${}_3$ superlattices

Abstract

The effect of octahedral tilting on the acentric structural transitions in AGaO${}_3$/A'GaO${}_3$ [001], [110], and [111] superlattices (A, A' = La, Pr, Nd) is studied using density functional theory. We find the displacive transitions are driven by two octahedral rotations modes (a${}^{-}$a${}^{-}$c${}^0$ and a${}^0$a${}^0$c${}^{+}$ tilting), with amplitudes that depend on the A and A' chemistry and cation ordering direction. We find the ground states structures of the [001] and [111] ordered superlattices are polar. The coupling of octahedral tilting modes through a hybrid improper ferroelectric mechanism induces the polar displacements and produces the macroscopic electric polarizations.

20 pages (main text and 4 figures) plus 10 pages (suppl. mat.)

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