Novel Intermetallic Chemistry: Approximants, Quasicrystals, and Rare-Earth-Metal-Rich Systems

点击翻译按钮获取中文摘要

TECHNICAL ABSTRACTThe principal goals of this research are to discover and characterize certain totally new types of compounds in unknown regions of metal-rich systems and to develop and understand their structures, bonding and properties. Pioneering explorations will continue to define new examples of aperiodic quasicrystals and their crystalline approximants, intermetallic systems with particularly low valence electron concentrations that exhibit unusual crystal structures and special electronic stabilities. The active metal (Ca, Ba, etc.) ? Pt, Au, Ag ? triel, tetrel (group 13,14) elements are typical ternary components. New chemical insights into their compositions, structures, bonding and special electronic stabilities will be exploited. New metal-rich compositions that exhibit different kinds of special electronic effects are also sought, e.g., electronic pseudogaps. Synthetic explorations together with physical characterizations will also examine new horizons and unexpected chemistry within metal-rich cationic networks of rare-earth and transition metals paired with main-group metalloid or nonmetal anions, of Te, Sb, or Bi especially. These phases are in essence the inverse of the condensed intermetallic ?salts? containing polyanionic networks and simple cations described in the first part. NON-TECHNICAL ABSTRACT The majority of elements in the Periodic Table are metals, and thus compounds formed between two or more metallic elements make up a large fraction of possible compounds, all other factors being neglected. Moreover, very little is known about most metal-rich materials, which are generally unique in their properties and structures relative to compounds made of other more conventional elements in the Table. We are seeking to extend and advance solid state and materials chemistry concepts and knowledge into unexplored regions of intermetallic chemistry, particularly those relatively poor in electrons around a few classical examples of special chemistry and physics. Quasicrystals and their approximants are examples of such special and contemporary phases. In a broader view, educational and research programs at the frontiers of solid state and materials chemistry around the world have over the years been broadened and strengthened by our research programs. Among those who have completed Ph.D. or postdoctoral research in these labs, 30 hold academic or National Laboratory positions in this country, and 24 do so overseas, these groups constituting of 50% of the total participants.