New Multifunctional Transition Metal Oxides with Correlated Electronic Properties

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Non-Technical AbstractWith support from the Solid State and Materials Chemistry program in the Division of Materials Research, the focus of this research is the synthesis and characterization of new transition metal oxides with low-dimensional, strongly interacting electronic properties to discover new multifunctional polar and magnetic electronic materials with fundamentally important and technologically useful behavior. The emphasis of the program is the detailed characterization of the structure and physical properties to understand the structure-property relationships. It has been demonstrated repeatedly that fundamental research of this type provides the basis for discovering new materials, which lead to novel phenomena and useful applications. The proposed work will impact the training and education of Postdoctoral fellows, graduate and undergraduate students in the PI's laboratory in the experimental synthesis and characterization of new functional solid state materials. Collaborative work of the PI with other scientists and condensed matter theorists nationally and internationally provides additional broader impact for the scientific training and education of students. These studies are expected to yield not only critical insight for the control of the properties of novel electronic and magnetic materials, but also to provide broader impacts for potential applications of the discovered materials in microelectronics and magneto-electronics for computers, sensors and communications. These are critical areas for maintaining US technological leadership worldwide. Technical AbstractThe focus of the experimental program is the synthesis and characterization of new functional transition metal compounds with strongly correlated electronic properties that are on the verge of electronic and structural instabilities, and to fine-tune the competing electronic interactions through the unstable region in a controlled way. Experience shows that materials with novel behavior are likely to be discovered, when lattice, spin, charge, orbital and other electronic interactions compete. Such competing interactions can lead to interesting and useful properties, including metal-to-insulator transition, magnetic ordering, spin and charge density wave instabilities, multiferroic, magnetoelectric behavior and superconductivity. In low-dimensional materials the interplay of competing interactions is enhanced. Systems of interest include: (1) Transition metal Ruddlesden-Popper (RP) layered phases, AO(ABO)n; (2) Layered double perovskites, AA'BB'O6; (3) Quadruple perovskites AA'3B4O12; (4) AA'BB' O6 new non-centrosymmetric corundum phases. These complex, strongly correlated electronic materials share the common feature of an interplay between localized and itinerant degrees of freedom, a highly variable conduction electron band-width, which may be tuned by changing e.g., the crystal structure, chemical composition, external strain and degree of disorder. The variability of band-width leads to a variety of important phenomena, including metal-insulator transitions (or sharp crossovers) driven by variation of temperature, magnetic field, illumination, pressure, lattice distortion and other variables. We expect that in the vicinity of these transitions the transport, electronic and magnetic properties will also change dramatically and will be tunable. The effort is a systematic study of unique synthetic routes including solid state, high pressure, "chemo douche" hydrothermal for the stabilization of new and interesting transition metal compounds. Crystal growth (essential to study anisotropic properties) of promising new phases will be attempted by e.g., flux growth, chemical vapor transport, and electrolysis. The characterization of properties by a battery of physical measurements including x-ray and neutron diffraction, electron diffraction and transmission electron microscopy, temperature dependent transport, specific heat, dielectric and magnetic properties measurements will be carried out.