MSE Colloquium - Prof. James Rondinelli
Date: April 18, 2014 from 11:00 am to 12:00 pm EDT
Location: Room 214, S.W. Mudd
Contact: For further information regarding this event, please contact Wesley Hattan by sending email to wjh2121@columbia.edu or by calling 2128547860.
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  James M. Rondinelli, Drexel University

"Versatile Abilities of Lattice Instabilities: New Design Strategies for Emergent Ferroics"



There are two main routes to accelerate materials discoveries for advanced electronic and sustainable energy technologies: serendipitous realization through conventional synthesis or computationally guided growth of novel materials through,
e.g., artificial structuring of bulk compounds at the atomic scale. Recently, the launch of the Materials Genome Initiative (MGI) at the national level has reinvigorated the search for new routes to accelerate the discovery of advanced materials for rapid deployment - the aim being to evolve a "hunter and gatherer"discovery paradigm into the cultivation of materials by design. 

Within this setting, and motivated by prospects of integrating perovskite-structured oxides into electronic devices to reduce consumer power consumption, 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 octahedral rotations common to perovskites oxides, I show these lattice distortions provide a new structural "sand box" from which to design and discover such ferroic phases (Figure 1). Bottom-up engineering of the transition metal octahedra at the unit cell level, is applied to realize ferroelectricity in artificial ABO3-structured composites 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-a-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 proposing new arenas for ferroic discovery.