In the search for new classes of multifunctional materials, ferroelectrics, in which the spontaneous electrical polarization couples strongly to other structural, magnetic, orbital and electronic degrees of freedom, is a challenge being actively pursued as a means to achieve electric field-controllable emergent phenomena such as ferromagnetism.
Although perovskites are often what comes to mind when discussing oxide ferroelectricity, the overwhelming majority of oxide perovskite--particularly those which have active electronic, magnetic and orbital microscopic degrees of freedom--adopt highly distorted, non-polar, ground state structures in which the BO6 octahedra are rotated about one or more of the crystal axes. Octahedral rotations, which significantly change the transition metal-oxygen-transition metal bond angle, are well known to control the emergent properties of a given complex oxide material.
A fascinating question that is only recently been considered in earnest concerns how to directly control these octahedral rotations with an external electric field. Our approach to this challenge is to ask the question, "how can octahedral rotations induce a spontaneous polarization, (i.e., ferroelectricity)?" By themselves, octahedral rotations cannot, but recent work by researchers has demonstrated that they can induce ferroelectricity in combination with certain cation ordering and/or hetero-structuring.
Credit: Created by Professor Nicole A. Benedek, UT-Austin; used with permission by The Journal of Physical Chemistry