Argonne National Laboratory

Materials Science Division

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John Schlueter - Description of Research

My current research interests lie primarily in the design, synthesis, and characterization of conductive and magnetic molecular based materials. Three specific topics currently of interest are:

1) Molecular Based Superconductors.

Layered, molecular-based superconductors are proving to be ideal low temperature reference materials for the higher Tc cuprates. We have pioneered a new approach for the synthesis of these molecular superconductors involving the use of large, discrete anions as the charge compensating entities. A major goal of this new direction is the preparation of isostructural series of charge transfer salts in which the physical properties can be fine tuned through anion modification. Through this methodology, structural control is placed in the hands of the synthetic chemist. This approach initially lead us to the discovery of the most tunable family of molecular superconductors known: k(ET)2M(CF3)4(solv). We have extended this work to encompass the incorporation of organic anions, thus crystallizing the first completely organic superconductor: b"(ET)2SF5CH2CF2SO3. This highly tunable structure is completely free of magnetic impurities, rendering it an ideal system for probing the subtleties of the superconducting state. Creative synthetic strategies and detailed physical property measurements are in progress to provide a detailed picture of superconductivity in these systems.

2) Molecular Magnetic Materials.

The goal of this research project is to develop structure/property relationships for isostructural series of molecular magnets which will lead to the design and synthesis of magnetic materials with transition temperatures suitable for applications. Specifically, our research is focused on three systems. The first of these are Prussian Blue-type solids which consist of [Cr(CN)6]3- building blocks and trivalent rare-earth metals. Secondly, whereas thiocyanate (NCS) has been used successfully as a ligand in magnetic systems, the cyanate ligand (NCO) has seen very limited use. We are exploring the use of cyanate as a superexchange ligand for molecular magnets. Finally, we feel that hydrogen bonding can be used as an elegant method to chemically couple magnetic centers together. To this end, we are exploring the use of the formate (HCO2) anion as a bridging ligand to synthesize structures of the M(HCO2)2(pyrazine) type.

3) Colloidal Superconducting and Magnetic Nanoparticles.

Recently, there has been considerable interest in the development of facile synthetic techniques for the production of colloidal metal and semiconductor nanoparticles. In large part, this interest stems from the remarkable size-dependent optical and electronic properties of these particles. Nanoparticle-based materials have also drawn increasing attention. The development of such materials, however, requires not only convenient methods for nanoparticle synthesis, but also methods by which these particles can be spatially organized in a processable matrix. We are interested in the chemical synthesis of superconducting and magnetic nanoparticles and the development of methods by which they can be incorporated into polymer-based matrices to yield novel, nanocomposite materials.


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