Atomic Scale Design of Polar Perovskite Oxides without Second-Order Jahn-Teller Ions.

Demands for low-power and high-efficiency electronic devices have spurred an increased interest in new ferroelectric oxides, which display spontaneous electric polarizations. There are only a few mechanisms, however, capable of producing ordered dipoles in solid-state materials. Using first-principles density functional calculations, we extend the current repertoire and identify the required rotational patterns conducive to "geometric" ferroelectricity in (A,A')B2O6 perovskite oxides with A cation order along [001]-, [111]-, and [110]-directions. For the polar oxides, we show that electric polarizations arise through a geometric, "rotation-induced" mechanism and are greater than those induced by spin-driven mechanisms. We also discuss the energetics of each ordered arrangement and explain how competing centrosymmetric phases can lead to potential complications in thin-film growth of these materials. Finally, we generalize these results to a simple set of structural chemistry guidelines, which may be used to design other artificial oxides without inversion symmetry. [ABSTRACT FROM AUTHOR]