The 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.
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.
Normal 0 false false false EN-US X-NONE X-NONE Quasicrystals (QCs) are very special, relatively electron-poor intermetallic compounds that exhibit somewhat mysterious structures and properties that must be considered indirectly in higher dimensions (6D rather than 3D for conventional materials). (The 2012 Nobel Prize in Chemistry was for the discovery of quasicrystals.) Fortunately, QCs also have some closely related but more conventional 3D neighbors called approximants (ACs). We have been pursuing new QCs through the discovery of new AC familes which also occur in about the same regions of composition space and generally with <2.2 electrons per atom. This stil leaves thousands of systems to explore, but chemical intuition is helpful regarding typical elements, conventional structures, clusters for example, and some speculation. A fairly rare structural family, an Mg2Zn11 type, had eariler given somewhat related clusters, and rather speculative theoretical calculations on such examples did reveal islands of extra electronic stabilities nearby. Chemical tuning plus X-ray powder patterns analyses did reveal what turned out to be new ACs, and further "synthesis-powder pattern" searching turned up QCs near most. About 10 new QC,AC were so discovered. These explorations were additionally valuable as they led us into in new regions of chemical space, places that chemists (or others) had rarely visited, if at all. Another major benefit of this (and other related work) was the discovery of the special roles that gold (Au) plays in bonding and stabilities of new things. Other systems first showed us that Au often gave unusual (one of a kind) compounds, or that the bonds to Au were unexpectedly short. Phase space around QC,AC regions isn't empty, but full of unknowns, because no one has looked before. The use of gold in some AC,QC successes gave other bonuses, which have led us into major explorations elsewhere with Au. Examples, only by formula, are Ca4Au10Sn3, SrAu3Ge, Ca14Au46Sn5, and Ba2Au6(AuZn2), also with other elements in place of Zn. The origin of Au's special characteristics arise with its 5d106s1 valence configuration and a particularly high nuclear charge at that point; "relativistic effects". Seek and you will find!
