Condensed Matter Physics Seminar

2 p.m., Thursday, April 17, 2003
Room 1201, Physics Building

 Controlling Kinetics and Mechanisms in Solid State Reactions using Modulated Elemental Reactions: New Compounds with Designed Nanostructure

David Johnson

(University of Oregon)

Abstract:  One of the first steps in gaining rational control of a synthetic pathway is the ability to avoid unwanted reaction intermediates or products.  We have developed a controlled synthetic approach to new solid state compounds which uses modulated elemental reactants to control composition on Ångstrom length scale.  If the layer thicknesses in the modulated reactant are below a critical value, initial interdiffusion of the superlattice reactant results in an amorphous reaction intermediate.  Nucleation is the rate-limiting step that can be controlled using the overall composition and "seeding".  Crystallization of this intermediate results in 100% yields of desired kinetically stable compounds.  This reaction pathway avoids stable binary compounds as reaction intermediates. We will show how information from known phase diagrams can be used to predict potential metastable compounds. Examples of new binary and ternary compounds made using this predictor that are only kinetically stable with respect to disproportionation will be presented.  Examples of nanostructured solids prepared using this approach will also be discussed.
Host:  Fuhrer
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