AVS 61st International Symposium & Exhibition
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI+MG-TuA

Invited Paper MI+MG-TuA1
Versatile Abilities of Lattice Instabilities: New Design Strategies for Emergent Ferroics

Tuesday, November 11, 2014, 2:20 pm, Room 311

Session: Development of Multiferroic Materials (2:20- 5:00PM) MIND Panel Discussion (5:00-6:30 pm)
Presenter: James Rondinelli, Drexel University
Correspondent: Click to Email
I describe in this talk the design methodology and theoretical discovery of a new class of “rotation-induced” ferroelectric materials. By tailoring the instabilities of the BO6 octahedral rotations common to ABO3 perovskites oxides, I show these lattice distortions provide a new structural “sand box" from which to design and discover such ferroic phases. Bottom-up engineering of the transition metal octahedra at the unit cell level, is applied to realize ferroelectricity in artificial perovskites superlattices formed by interleaving two bulk materials with no tendency to such behavior. This emergent, chemistry-independent, form of ferroelectricity – octahedral rotation-induced ferroelectricity – offers a reliable means to externally address and achieve deterministic electric-field control over magnetism. I discuss the required crystal-chemistry criteria, which are obtained from a combination of group theoretical methods and electronic-structure computations, to select the compositions and stoichiometries giving polarizations comparable to the best known ferroelectric oxides. Much rarer in crystalline materials with an electric polarization, however, is the appearance of a ferri-electric (FiE) state, vis-à-vis ferrimagnetism, where local electric dipoles of different magnitude are anti-aligned to yield a net non-zero electric polarization. The underlying reason is that the long-range Coulomb forces in oxide-based dielectrics favor the cooperative alignment of all electric dipoles in the crystal through cation displacements that occur against an oxygen ligand framework. I conclude by describing our recent discovery of a first-order, isosymmetric, transition between a ferrielectric (FiE) and ferroelectric (FE) state in A-site ordered perovskite superlattices and offering new areas for ferroic discovery