New Intermetallic Phases with Matter Occupancy Waves

Cornell University, Ithaca NY

Investigators

Abstract

This project will focus on new intermetallic compound discovery, structure determination and property measurement, effectively coupled with quantitative computational methods and qualitative theory to develop experimentally productive structural and bonding models. The focus is on intermetallic systems where it is not clear whether main group element-metal, metal-metal, or element- element bonding dominates structures and properties. This class of materials has been chosen because they are difficult to understand and because these materials possess an unusual balance of bonding trends that could very well lead to materials with novel properties such as matter occupation waves and sublattice shear patterns. A focus of the synthetic efforts is substructure-superstructure relations. Crystalline superstructures provide intrinsic clues as to the bonding. If a range of superstructures appears for a class of materials, that is often a clue that the structures are in some careful (and easily perturbed) balance of determining physical forces. Phases will be studied in which transition metal -main group interactions dominated the structure (Nowotny chimney ladder phases), metal alloys involving both electronegative and electropositive atoms (Copper-Zinc) and square net systems with reduced energy gaps between the composing elements (ternary rare earths and a variety of ternary compounds with alternating transition metal and main group elements in the lattice). These systems do more than just force one to go beyond the Zintl concept, they also bear structural features in common. All these systems exhibit matter occupation wave superstructures, a type of ordering which can not in general be treated by the traditional charge density wave arguments. There are also connections to problems of crystal growth, of ionic conductivity and a possible new phenomenon of sublattices moving or shearing through each other. New theoretical ways at looking at such superstructures will be developed. The goal is to full couple experimental and theoretical work. [The graduate students supported by this research may be reasonably expected to have elements of synthesis, property characterization and theoretical computation in their theses.] %%% Structure, composition, property correlations of these new classes of materials may exhibit interesting magnetic, superconductivity, and ionic conducting behavior. Students will be trained in solid state synthesis, property characterization and theoretical computation and modeling, all of which are areas of high relevance to current academic and industrial job opportunities.